The way I see it, the entire stock sound library market was dominated by a few handful of companies throughout the 90's and most of the aughts. Sound Ideas, Hollywood Edge, and not much else really... If you go check out the websites of some of these companies the web layouts make them look like they haven't been updated since 2001. It just seems like a sign of complacency from all the years of complete market dominance.
It has gotten a lot better in recent years though with many smaller SFX companies popping up and offering high quality, more specialized stock libraries. Like, you could get one with just tons upon tons of different metal clang noises, instead of having to rely on the same douzen or so you've heard a million times from the more generalized old libraries. They are often cheaper and provide exponentially better value as well. Last time I looked, the old Sound Ideas libraries were still ludicriously expensive, and you don't exactly get much value out of them these days since overuse has greatly eroded their uniqueness, and more modern libraries are often available in 96khz rather than 44.1 which is a great boon for sound designers using them (you can do stuff like pitch them down heavily and still retain a lot of brightness, since those previously inaudible super high frequencies are also shifted down into the audible spectrum)
But a lot of studios still rather use their old legacy libraries instead of investing in new ones. You'll most often hear them in cheap TV productions. Even if they employ freelancers that might have access to different stuff, they'd rather they just use the same old libraries they already have the rights for internally so they don't have to bother with multi-user licenses and such.
