Yep, I won't deny that the survival crowd can be somewhat of a fickle one and there certainly is a flavor of the month feel to the genre, but there are legit reasons for it. Rust, like Squatc4 said, is a completely different beast. That's your typical survival game and while it did wane in popularity, it has little similarities to the king of the hill games.
Culling was wildly popular upon release, but then the devs apparently messed it up, according to the reviews. By the time I got it in a bundle it was essentially dead and shell of it's former self. H1Z1:KotH had a similar trajectory - great initially, but poor dev decisions and a lot of monetization/microtransaction/etc. made it drop in popularity even before PUBG came out. I've also heard it referred to as a more cartoony PUBG.
PUBG could mess things up eventually, but I sort of doubt it at this point. They know what's working. They're selling tons of copies at $30 a pop and getting a lot of market loot with cosmetics. There's no reason to do something stupid like introduce P2W type loot or tweak the mechanics too much. TBH, I see it possibly becoming one of those CS type franchises where if you want a certain type of game (KotH) then you just buy the latest version of PUBG, but only time will tell.
These games are relatively cheap so that even if you buy them on release and play them, you don't get "ripped off" in any way. And if they really hook you, they're a great value even if they eventually dissolve into a mess.