Wow. Great question. Huge and sweeping.
What's missing? Just about anything that's not directed at predominantly white, middle-class guys with lots of disposable income and heaps of free time.
Getting into the hobby? Cheaper books, less reliance on expensive on-ramping materials, lighter rules, less math, less homework, more pick-up-and-play, more solo RPGs, and a lot of other things along a similar vein.
Engage more? Mostly the same as above. Less expensive hobby overall with less math and homework, lighter rules, pick-up-and-play, solo play, etc.
Underserved? Anything that's not action-adventure power fantasy set in a fantasy world. Games exist that aren't those, but they're decidedly niche and practically invisible. The audiences that like those other kinds of games are therefore underserved. Sure there's a smattering of sci-fi horror mystery and the odd western, but compared to fantasy they're a tiny fraction of the hobby. To say nothing of every other genre. Romance, cozy, non-violence, community focused, community building, etc. Yes, I'm aware there's like two games that might handle one of those, but that more proves my point than disproves it.