I've speculated that D&D is the success that it is because its current mechanics better support the kind of heroic gameplay that has predominated since the mid 1980s while being more streamlined than other modern versions of D&D.
TSR-era D&D had streamlined mechanics (well, aside from THAC0 or a lot of 1e clunkiness), but its classic dungeon-crawl and attrition-survival chassis didn't really enable heroic-style gameplay. Pre-5e WotC D&D better supported heroic play but was very crunchy.
5e basically has the advantages of both. It's baby bear's porridge, chair, and bed, as it were.
I also think this sets up a positive feedback loop with the pop culture, D&D streaming, and such.
E.g. I don't think Critical Role could have become such a sensation with any other version of D&D (or, if memory serves, Pathfinder, which I vaguely recall reading that the group might have been playing before Geek & Sundry approached them about the live play streaming show).
Or, e.g. I don't think the interest in Stranger Things would have helped D&D if the game had the unforgiving chassis of TSR days or the fiddliness of 3.X/4e.