What items are people buying and why are people buying things from the shop?

I personally have not spent a cent on this game. I am holding two gyms and get 20 coins a day and am perfectly fine with that. I am almost level 30 and have no desire to get much higher than that because I am playing to complete my pokedex.

I would consider buying incubators, but I never end up hatching anything I need (if it's not grimer, tangela, or a 10k, I don't need it anymore, and I know I'm not likely to hatch either of those). I don't see the point of burning through eggs if I never get a 10k egg that I could use.

Lures don't seem attract any of the pokemon I have left (only commons). Same with incense. I don't really need lucky eggs because I don't really care about leveling up (especially after 30).

I saved up for one pokemon storage upgrade after they released the baby eggs.

So how is Niantic making so much money? What are people buying? And why?

If items increased the chance that I'd catch something I didn't have yet, I'd probably pay for them at this point, but they don't, so why are people still buying stuff?