why expensive streamers

I've heard bigger differences between music servers than between DACs. 

Within the context of my digital music playback system, which involves using Roon to stream Tidal and Qobuz, and to play stored music files, my hierarchy of  differences I hear is:

• Server/Roon core: almost no differences heard between servers
• Fiber optic vs. Ethernet: little to subtle sonic differences at most, but not reliably discerned
• Switches, on-line tweaks, and decrapifiers: no reliably heard differences
• Streamer/Roon endpoint: more substantial sonic differences and the ability for some streamers to significantly improve sound quality
• DDC: Little to subtle sonic differences noted, at most
• Digital cables including USB:  small differences between coax, AES/EBU, and USB, but very little to no differences between different cables of the same type 
• DAC: Each displays its own sonic flavor and can sound substantially different from each other

In summary, I have noted differences in the sound of streamers and DACs, but not  much with anything else in the digital chain.

I don't have a streamer or a DAC and I am absolutely clueless but based on what it does, it sounds like the only reason why cheap streamers sound worse than expensive ones is because they are poorly designed and "create" issues. There should be no noise, no timing issues, a streamer just moves packages like a conveyor belt at the airport. The software would have only one way to put the packages together, in either a 500 dollar or 5000 dollar streamer. 

But again, that's just my wearing an IT hat, knowing nothing about music streamers.

I guess I lucked out. In my first foray into music streaming, I chose the Cambridge Audio CXNV2, and it had the exact sound I was looking for. Or, perhaps it sounded the way I wanted it to sound because I had already achieved the sound I was looking for in my setup, and it was neutral enough to fit right in. Food for thought.

@jeffreyw - But of course :-)