I remember these tire names and I actually had the X-Ones on a car in which I ended up selling. So, their memory was short for me.
In terms of longevity, this is somewhat subjective. You & I could have the same vehicle/engine/tire size. And both of us could get different lengths of tire tread life depending on driving style/multiple drivers etc.
Also, these tires may have had longer warranties of months owned. Instead of the standard 4 or 5 years of warranty(down to 2/32nds, they may have given 6 or 7 years. IIRC, the G/Y started out at ~ 12 32nds instead of 10 32nds...Just saying!
Another factor that comes to mind is, maybe they weren't profitable enough for the companies to keep producing...or the warranty killed them.
Keep in mind too, that the market and technologies have changed and the names of the tires have changed to reflect that. There are a ton of reasons that these tires are not with us any longer.