Basically, this. If you're looking for a reason to play "D&D or any other system", then your reasons vary widely. If you're looking for a reason to play "D&D specifically", then your rational reasons narrow to something like: optimization, popularity/familiarity, ease of using setting-specific fluff. (There might be a few others but those are the main ones I can think of.)
So one of the biggest differentiators for D&D is optimization, though that doesn't define as much of the total play experience for someone new to RPGs as a whole.