Probably my favorite genre.
First off, we're basically in the midst of a DRPG Renaissance, maybe at the tail end of it. Legend of Grimrock 1+2, Might and Magic Legacy X, Bard's Tale 4, tons of mobile ones [The Quest, 7 Mages, etc], tons of lesser known steam ones, Star Crawlers...
The reason the sub-genre isn't as popular as popular as some is because, well, it's intentionally niche. Much of the enjoyment is based on resource management, mapmaking, problem solving, and risk management. These aren't things most people like.
That's not a bad thing.
We -should- have genres that not everyone likes... because not everyone is the same. I'm extremely happy some genres exist that tailor to what I like in a game, even though I know they'll never be super popular. I don't want those genres to change to become 'more inclusive', because then they wouldn't appeal to me in the first place.
People complain a drpg is 'always in a dungeon'... I mean, what do you think the D stands for? That's the point! Complex dungeons with complex traps. Lose your situational awareness, get lost, get party wiped. Go to deep without enough supplies? Party wipe. This is a good thing.
Keep in mind most of the discussion here is around japanese DRPG's (Elminage, Etrian Odyssey, Stranger in the Sword City etc) which are all still stuck in the Wizardry 1 rut.
Western dungeon RPG's evolved past that decades ago and are still trucking along just fine.