Assuming where you live has deductions anything like where I live, they are taking home a lot less than $370. And of what they are taking home, D&D paraphernalia is in competition with everything else that they could spend the money on, same as for everyone else. Are they saving for college? For a car, or gas for a car, or insurance, or repairs? Do they have to buy essentials? - sadly, that is true of more teens than we might like to think. Or maybe they are weighing it against other entertainment options, cool clothes, etc.
My point is that teens, just like the rest of us, have a lot of different demands on their wallets, and each has unique circumstances. For some, I'm sure that dropping a few hundred bucks on D&D stuff is no big deal, but that is definitely not true of most teens that I know. I work at a private school, where the kids are almost all well off, and they still play D&D using scraps of paper and random tokens for miniatures, share books (and my DDB subscription) and are generally scrimping and saving for college.