That can't possibly be the case. Why I swear it was just a few years ago I was grumbling about the fact that there was really no need for a 4th edition.
/me checks the publication date of 4e GURPS
Huh. 2004. Welp, I'm going to find an ice floe to put myself on and float off into the ocean now...
I think what's out of favor is the pairing of complexity and toolbox that GURPS has. If you buy the GURPS rules you don't really get a "game" so much as a collection of rules that you can put together to make a game. That was a more popular thing back in the 80s and 90s than now.
I think "universal" systems are still being used, but they're being used by game developers who adjust the rules for you rather than providing a toolbox for you to make your own game. Like all of the Powered by the Apocalypse or Forged in the Dark games, or the Gumshoe games that Pelgrane puts out. Even Steve Jackson Games does this by putting out games that are "Powered by GURPS" that include the rules and setting together instead of just being setting books. (I would actually love to see them put out Infinite Worlds as a standalone game powered by GURPS personally. Pare the rules down to just the ones you need for the IW setting, include the appropriate character templates to choose from, etc.)