Which isn’t entirely true. A lot of people like RuneQuest for it’s mythical feel.
Well, I like Glorantha for it's mythic feel.
I'm not sure watching Rurick and Uras miss eachother in a bar fight is terribly mythic. ;P
I liked RQ because it was a great system for it's day. It was skill-based, classless, and fairly open about what you could play. Many races were at least theoretically playable, you needn't choose between being a magic-user who can't swing a sword or a fighter who will never be able to use magic - anyone could learn to use any weapon, anyone could learn battlemagic - anyone could wear any armor they wanted to (except iron, of course). Only at the 'rune' levels did you get into anything like a class, and even that was earned, and not necessarily mutually exclusive. The prevalence and attitude towards magic items was very different, as well.
A lot of people just feel it’s better for adapting fantasy fiction - like Game Of Thrones for example - without having to get bogged down in artificial arguments about what Class a character is, and so forth, or fixated on gaining XP and levels. And for that reason it has everything to do with whether D&D is as good a system for fantasy as others that are available.
Fantasy Fiction like the anyone-can-die-at-any-time Game of Thrones, yes. Other sorts, maybe not quite so much.

RQ could be a little brutal and less than heroic in some ways, which was ironic, given the backdrop of Glorantha.
I have. It works really well.
D&D's style is mostly just treasure hunting, paranoia, and wildly overpowered magic (items & casters). The last is a little harder to do in early RQ, but RQIII could presumably have handled it.
I think that D&D has become sort of a genre of its own, with its own tropes, assumptions, and expectations.
I've heard that a lot, and, while I tend to agree, it doesn't really let D&D off the hook for failing to handle other genres. Especially since, as the first/best-known FRPG, people inevitably /try/ to use it for other genres.