Why are older tubes so much sought after

I echo all who said that they simply sound better but are at times in poor working condition. The NOS tubes are virtually gone except for the JAN military surplus made in the 70s and 80s believe it or not The occasional treasure found in a repair man's attick or tubes nobody wants.
What you find are used tubes that test well on a questionable tube tester because that too is over 40 years old. Yes I know you can get it to spec by sending it to a pro. My experience is that tolerances drift easily with these old (explective).
In essence I have learned in my collecting tubes that it is truly just a hit or miss on ebay but with dealers you get to know, they will sell you only tubes that they expect to hold to spec longer than other thus "good" tubes. There really is the occasional good tubes is all I sell dealer but that is rare.
Old stock tubes are also often superior because of they afford you variety. Tubes in their hey day came from many many brands, that had there own recipe, to actually give their tube a certain flavor e.g. "Our tube is better than ordinary tubes find out and you will only smoke Mazda tubes." (All tube making facilities secretly were and are owned by Phillips. Yes I know that all brands were not made by Phillips and please I am not bashing Mazda) thus you get different sonics with the brand you buy. So it gives you a tone knob on our very simple path amps and pre-amps.
However you still need guidance from a person who truly knows what that particular tube sounds like compared to others.
For example one can make generic statements about a particular brand such as Mullard such as " they are warm colored." Simply put this person is correct, but not all the time. I use a military variant for a 6922. This tube is made by Mullard and is a drop in sub. This tube is not warm and fuzzy it sounds very fast and very clean with a powerfull voice comparable to a German tube. ( The Mullard CV 2943s)
Trelja I have a few pairs of 7199s but all brands are made by Amperex no matter what the label is. I think so anyway. It could be Sylvania I have to find out. Non Trelja people please do not write asking for these tubes -thanks

I will top Trelja's offer. I will provide the Sovtek tube of my choice. I assure you it will be a commonly used audio tube. I will give you 2 for each "tests good, quiet tube pre 1970 from the 6922 family or "tests good and quiet NOS" 12 volt miniature double triode of the following 12AX7s, 12AT7s or 12AU7s. The offer is good until my supplies last. I will consider offers of GEC/MoV and Mullard or other NOS power tubes. Trelja I will share the bounty with you.
I would like to point out that TRELJA is not a snooty guy. He introduced me to the Sino 12AX7 9th ed. or "C" version, which cost all of 5 or so bucks each and I use them. Further he recommended I use EH tubes in an application that have been nothing short of fantastic.
I can probably get some fatter honkinger 6SN7s for him than the RCAs but he likes them, so why fight. But If I were him I would seriously consider my offer of CKR/VT-231 or civilian Ken Rad 6SN7 GTs. No N7 has better bass energy.
Rodman I know you like the Tung Sol RPs and the tall Ws above all comers. I own 3 pairs of each and still say, quite confidently, that in terms of bass alone and only, the Ken Rads are better. Overall I am happiest at the moment with the Ws and won't be trading any of those.