Q: Why did What Ifs and Elseworlds use to be so popular? And why don't we see them much anymore? -- @TheKize
A: I don't want to reject your premise outright since I think you're onto something here, but I also think it's worth pointing out that we're not exactly suffering from a lack of alternate-continuity stories, either. Multiversity, Convergence and Secret Wars were all based at least partially on the idea of exploring and playing around with the same kind of stories that didn't quite happen. If, however, you're talking about those specific brands, the What If books and the Elseworlds imprint that showed up on so many comics, then you're right.
For the most part, I think it just comes down to a simple swing of the pendulum back from oversaturation. There were a ton of those stories, and as is usually the case with these things, publishers just decided to put 'em away for a while. But there's another reason, too, and it has a lot to do with why so many of those stories exist in the first place.