Often designers (at least competent ones) are forced to take a broader view than people who play or even GM games. And in cases where they don't, its often extremely obvious.
I would also add that D&D (especially 5e) engages in extensive playtesting and market research in terms of surveys that most games are unable to. Which allows them to iterate and release "broadly popular" products.
Being broadly popular doesn't make you "good" or "well-suited for everything," but it does help ensure that you are giving people what they want and will get paid for it.
