I think you're mistaken to dismiss the gameplay loop just because video games do it better. The crux of your response is built upon that dismissal, but I couldn't disagree more with your assumption.
Sure, there's an argument to be made for video games doing the loop better.
There's not really an argument there. It's a fact. Video games simply do it better. Your assertion was that the game play loop was a draw. Okay. So if that game play loop is the draw...why do people play games that do a substandard version of that same game play loop, i.e. tabletop RPGs. The computer can give you scrolling damage over your avatar's head, give you scrolling healing over your avatar's head, and give you scrolling XP gains over your avatar's head. If your argument is the game play loop is a "reward center of the brain" addiction mechanism, then clearly video games do that infinitely better. Tabletop RPGs have to have a Referee calculate those numbers and dole them out. That takes time. It's usually done at the end of a session, if it's done at all. Doling out specific XP rewards that is.
However, it completely overlooks the fact that even the best CRPGs are lacking the strengths of TTRPGs. Namely, freedom and real intelligence behind the world. A DM can respond in ways that a computer simply can't, since computers run programs and programs can only do what a programmer programmed them to be able to do. If the programmer didn't program in a way for you to try to kick in doors, then there's no way for you to do that, irrespective of how much sense it might make to do so.
They arguments are not connected. One argument isn't predicated on the other. RPGs are infinitely better, at least in theory, in that regard. But again, that is a definitional trait of tabletop RPGs as a whole, not D&D specifically.
The strength of D&D is the gameplay loop within the context of that freedom and real intelligence.
Again, that game play loop is not unique to D&D. Lots of adventure RPGs have it. And again, the freedom of choice is a definitional trait of
all RPGs, it's not unique to D&D.
And, I think, that is also why players often respond very poorly to bad railroading techniques and the like. Because once you start down that railroad they really are better off playing a video game. You hear this sentiment not infrequently when the topic of railroading is raised (if the DM is going to do that, I may as well play a video game).
Or read a novel. That's one I hear more frequently. And I agree.
I think that you could argue that there are some other TTRPGs that do the loop just as well as D&D, but none (IME) that are vastly better WRT that loop. Add to that the fact that D&D has a natural inertia from being many people's first game and, if I'm right about the loop being a significant reason for players staying, it seems quite reasonable that they continue to play D&D, even if they try other games as well.
I think you're wrong about the loop. Lots of games have it. It's mostly the inertia of D&D. It's popular because it's the most recognized name in the space. It's largely the only recognized name in the space.
I don't disagree that people play D&D because other people play D&D. That's certainly a part of its inertia. However, I think that if that were the entirety of it, you'd see far more people abandon D&D for "better" games in the long term. Most long-time gamers I know have played other games, despite that D&D is often their game of choice.
It's the inertia. Sure, you could go play some other game, but playing those is orders of magnitude harder to find players for. It's easier to simply backslide into D&D as the default state.
Your food metaphor from earlier is flawed. There's a not-insignificant amount of overhead in learning a new system.
It depends
entirely on the system.
Here. Let me teach you a game system.
"If the outcome of an action isn't obvious from the fiction, roll opposed 2d6. Higher roll wins. Negotiate ties."
There. Now you've learned a new game system.
Now, tell me how hard that was and how much it cost you besides the few seconds to read the sentence?
It's akin to if, before dining at that fine cusine restaurant, you had to take a 101 course on fine dining at your local college (or at least a weekend seminar). Sure, you can learn while you play if someone knows the rules, but someone has to be the first to learn them so that they can teach it. Moreover, everyone is likely to have a better time if they have at least some familiarity with the rules, because then you can focus more on enjoying the game and less on learning the rules.
Not all games have systems as complex as D&D. There is a whole universe of games with drastically less complicated rules. If you spend a few minutes looking, you can find games where the system is less complicated than a fast food chain's menu.
IMO, people stay with D&D because it is fun.
And the inertia. And because their friends play. And because...and because...
It's not just one thing.
