I'd agree with you, if we were talking, say, Fate — something actually flexible and hackable that doesn't come with a bunch of stupid assumptions.
D&D on the other hand is like the opposite of a hackable system.
It is comments akin to this that I think the OP is reacting to.
Familiarity > System.
...
"Because I don't want to." is a valid personal choice.
This post (I'm snipping the most relevant portions) really does seem to answer most of the thread. IMO.
The OP asked, at the end, the following:
So, for me, "you'd be better off playing a game that is made for that" usually rings hollow. What about you?
I think that's true for a large number of people in all sorts of endeavors. Talk to someone who is a fan of some sport (as a spectator) and try to convince them that some other sport is "better" to watch. Go on. Give it a shot. Or convince someone who drives an auto transmission CUV/SUV that if they want a real driving experience, they'd get a sport stick shift. Heck, it's hard enough to convince Chad that he shouldn't be using a hammer when there are much better tools ... but hey, Chad has a hammer.
People gravitate toward the familiar. There's nothing wrong with that. Moreover, the issue with these types of conversations often is that it is people talking past each other. Primarily because people like what they like, and are used to the things that they are used to. Truisms are true.
More often than not, there can be undercurrents of elitism, or some type of snide "You're doing it wrong," when it comes to playing D&D. For example, saying that D&D is based on stupid assumptions (as above). But that's not uncommon in many fields; Taylor Swift is going to be popular, and no matter how much you try to convince someone that Lou Reed's Metal Machine Music is a masterpiece that deserves their rapt attention, you're not going to get very far with most people- especially if you're doing it on a thread with Taylor Swift fans.
There are many great TTRPGs out there. But the pull of D&D will always be because of its size, its history, its scope, and its familiarity. You will almost always find it easier to get a group together for D&D, and if you move to a new area, you can almost always find a table playing it.