Because magic words such as vintage, warm, classic, tube, old school and other mumbo jumbo have been indoctrinated into the guitar and bass crowd as being key to getting a good sound.
So naturally gear that checks those boxes is going to sell regardless of price or value because we need it to sound good.
Why would I want the newest most sophisticated digital power section and features if it can't reproduce the sounds from 50 years ago that are the benchmark of good sound?
It's not like most recordings and big show audio equipment is going to run my bass DI in the cleanest possible way through the most sophisticated digital equipment available now. Right? Over my dead body.
Maybe you should take a look at the synthesizer market, which makes bass players look like troglodytes.
Back in the 1980's digital (Roland D-50, Korg M-1) became all the rage and they took the knobs and sliders off the keyboards because well you just programmed in what you needed to do right?
Well then the knobs started to make comeback, albeit on digital keyboards.
Then (late 1990's) physical modeling of analog became a big deal, big big deal and became a big part of the market.
Well at the high end of the market people started coming out with ACTUAL ANALOG synthesizers and those were successful.
Now there is quite a business in real analogs, to the point where the guy from Sequential Circuits (Prophet 5) bought the rights to his company name back, and now he has teamed up with the Oberheim guy and that company (the new Sequential) has a wide variety of mostly analog products.
The thing is the old school guys want to go back to that, and the new guys with new styles of music figured out the analog stuff not only sounded good, it allowed a greater interaction with the gear in real time.
Given the vast majority of bass players are using tones that have been around for 25 - 65 years, and the fact that all the styles of playing have evolved to a standard set of styles, there is no big market or desire to create a bazillion ways of doing things when the existing interfaces and amp designs work just fine.
The departure from this of course is Class D, but that's more a weight and power convenience factor.
The existing amp companies could have put really complex programmable front ends on these products and gave players the ability to create a million and one sounds, but the nature of bass does not really require that.
As far as the PA systems with their "sophisticated digital processing" go, well those systems are just replicating what the analog systems before them did. Obviously with greater control and precision but you are mixing a band in a venue which is WAY more complex than just playing bass on stage.
A modern Porsche 911 is in most ways (well besides the weight) far superior to an old school air cooled 911 but guess what people want? That old school air cooled 911 because it rewards the drivers in ways a modern, do it all with computers 911 cannot.
That's why people will pay $500,000 for a 2.7 RS from 1973 because what it brings to the party the modern car and try and replicate but frankly it does not.
Too much gingerbread for when all you want to do is drive an engaging sports car on a nice twisty road.
Analogeezer