This topic is often a good example of how people are more emotional than reasonable.
Someone will complain about all the things they don't like about DND, but when presented with alternatives balk and stick to DND. The devil you know, the comfort of the familiar, whatever.
Which is fine, I guess. We all do that kind of thing. I'm just as emotional as anyone else.
Learning a new RPG system is a big time sink. Maybe if you keep searching you can find one perfect for you, but it's easier to stick with the most famous one that everyone else already knows, and then add in tons of homebrew to fix the flaws.
If the extra enjoyment of a new RPG isn't worth the cost to learn more systems until you find a better one, it's rational to stick to D&D. Sunk cost fallacy is when you stick to it even though it's not rational.
It's probably worth learning some simple systems, but if you want crunch, is it really worth going through the effort of learning GURPS even though you don't know if you'll enjoy it any more?
Though the biggest problem is finding someone else to play it. Everyone plays D&D, so even if it's not as good they'll stick to that. I could learn a new system and enjoy it, but it's all for naught unless I can find other people to play it with me.
I concede that it's hard to find people to play other systems, but not impossible.
I don't think "I shouldn't read this system because I might like it less" is very sound. If you applied that to everything, no one would try anything new. Why listen to a new band when Mozart is fine?
I will die on the hill that DND 5e is actually pretty bad, though. It's complicated in all the wrong ways, the combat is surprisingly shallow most of the time, the adventuring day tries to force it into very specific cadences, it's shallow in its customization, it has a martial caster divide problem, the math is bad (flat probability can fuck itself), the magic system is incoherent, its support for the non combat "pillars" is lackluster... Pretty much every single part of the game makes me grind my teeth.
The only thing going for it is it's popular, and it's shallow in some ways that sometimes make it hard to make an ineffective character.
Honestly 5e has a bit of an identity crisis. It's trying to go just there enough to support players who want a more generic fantasy adventuring game, and just trad enough to not scare off the people who want the D&D Experience:tm: as it was in the 80's.
You'd be surprised how fast and easy to learn TTRPGs can be. Compared to what's available, DnD 5e is actually on the crunchier side (upper mid range overall)