They were great examples of what an arena shooter should be. Smooth movement, balanced weapons, well designed maps. The people who had experience with arena shooters liked them. Most new players did not want to get rekt for months on end while they learned the basics, however.

Only in the rather reductive sense of “the vast majority of gamers are into other genres now”.

Popularity and quality are two very different things. There are many brilliant games that simply didn't get much attention simply because of luck or attention got dragged somewhere else.

It can also mean the market has shifted which is more the case imo.