Why stream?

OK, I've been around the low end of the high end for 40 years, but the learning curve for digital audio has been steep. Needing a better DAC, I acquired a Cambridge 851N and started streaming. Yeah, this device is now Tidal-friendly. But Tidal streams at 44.1kHz, while Cambridge plays everything from USB -- Tidal, Spotify, Pandora Radio, iTunes library -- at 96kHz. Last night I used Spotify to find and play obscure old stuff listed on cassette tapes I made from 1975-1989. The sound (better amplification and speakers now, of course) was revelatory. Rather than exposing a thousand flaws, in most cases the Cambridge DAC/USB found unsuspected delights in these old (NON-remastered) recordings.

So, my question is simply: why stream when you get better sound from USB? I know Qobuz does 96, but no way it can match my library, and it can't beat USB from Spotify, which found every selection except one obscurity from De Danann, which I probably mistyped anyhow. 
 I am not sure what your issue is.  You enjoy a streaming service such as Spotify, for sound quality as well as for catalog and ease of use.  What is the issue?
Believe I was misled by a sales pitch implying higher-than-USB fidelity. Thanks to you I now see that streaming hi-fi has only been playing catch-up, and everybody else knew this. Gracias for the orientation, which is exactly what I had come looking for.

Hi-Fi streaming is here....if you have access to Qobuz streaming, sign up for a trial. They offer the best quality (upto 24bit/196kHz) streaming at this time. They may not have the vast catalog as Spotify but they are ramping up their library since their US launch. 
To answer why stream.....if you don’t care about exploring new music and content with enjoying your ripped collection and then streaming doesn’t make much sense for you.  
Not trying to be pedantic, but the word streaming can mean a few different things.  One can stream their own physical content that has been transferred to a hard drive (CDs, downloads, digitalized lps or cassettes, etc).  One can also pay a streaming service.  The service owns the content and a fee is usually paid monthly to access their catalog.  You seem to be only using the second definition.
  I gather that what you are saying is that a salesperson convinced you that a paid streaming service will sound better than the best reproduction of physical media.  As laltk is mentioning, there are are different qualities of paid streaming.  Most streaming services use a a compression scheme, to save on bandwidth.  Some services are of offering higher quality streams that approach or in the opinion of some individuals exceed the best reproduction of physical media.
.  The first services around 20 years ago used very severe compression.  When mp3 came along it revolutionized streaming (Apple and Spotify both use different compression schemes that are similar in quality to mp3, so the term mp3 is usually used to refer to all of them).  This is because most people cannot tell the difference between mp3 sound and a CD, even though mp3 discards over 90% of the Audio data contained on the CD.  This then can be the source of many a marketing pitch, as mp3 does sound a lot better to most people than a source such as YouTube, which may perhaps shock a listener of our generation (assuming we are contemporaries, I am 61) in that it has been the most common way for people to access music over the past decade.   Audiogon is an audiophile site, so it caters to those of us that can hear a difference between compressed and uncompressed sound.

  Rereading OP two posts, I see that he keeps referring to “usb sound”.  Keep in mind that there are different ways to transmit digital data.  usb was originally created for multiple uses, with transmission of audio being not the first priority.  It delivers the digital stream in packers instead of one continuous flow.  The other digital transmission schemes (Optical, also known as toslink, and coax, also known as as S/PDIF, are the most common) deliver a continuous flow (stream).  Wireless transmission is known as WiFI.
Thanks, everyone! Very helpful on all fronts. Yes I am one who can hear (and dislike) compressed formats, yes I am of the over-60 generation, and yes I will compare Qobuz -- maybe today or tomorrow as time allows.

Now, as for discovering new music: that's why I use FM radio and Pandora algorithms. (Famous example:  Fountains of Wayne "station" leads to Keane to Guster to Shins to Boy & Bear/War on Drugs/Wiretree). The algorithms can deduce my tastes, whereas I find Tidal's and Spotify's suggestions rather random (and, for Tidal, highly hip-hop biased).
If you use the premium service of the big boys, Pandora, Spotify, quality for simply listening while doing other things is fine. By far, Spotify will give you the most control and variation in your music with song stations, artist stations, playlists, etc. Pandora is decent in this category. Qobuz is definitely tops in quality for critical listening, but even that can be limited depending on how you stream (iPhone, direct, streamer etc.) and I agree Tidal is definitely Hip-Hop oriented, but that would be expected given it is Jay-Z's baby (mostly). As competition increases so will services/quality. Streaming is here to stay though, and is a great way to easily access gobs of music that wouldn't necessarily be available otherwise.
Very helpful. Thanks to above explanations I'm getting my bearings in this new (to me) world of streaming. All digital sources are played through the streamer/DAC with balanced XLR output to preamp, and all streaming is for critical listening except when streaming FM radio because analog signal is down. Like this morning.
One more thing, also compare the streaming over WiFi vs wired connection to your Cambridge Streamer / DAC. Many here, including myself found hard wired connection sounded more dynamic and cleaner.  
Most DACs sound a bit different through their difference inputs, and streaming DACs are no exception. Which input will sound better depends not only on the DAC design, but also on the component feeding the DAC and, some say, the cables. So it would not be wise to decide what system structure is superior in general, based on one DAC in one system.
lalitk, I agree, USB, as you say, more dynamic and cleaner than WiFi. mike, will definitely test other variables like running CD through Cambridge into preamp Aux. Macbook Pro with Jitterbug is the source for USB and all WiFi. May also mount TV above and run optical to the main system, so all Cambridge digital inputs will be tested.