It’s a matter of time before they acquire the top app or two and block the rest.
Apollo recently moved some push notification features behind a subscription to cover ongoing costs, separate from their "Pro" one time in-app purchase, so I think Reddit is at least taking a cut from API usage by other clients.
I'd be happy to pay them, but I actually don't WANT push notifications, posting from the app, or any of the other stuff that encourages websites to pull you in deeper.
And the only reason I even use Apollo is because mobile Reddit is a nightmare UX. Literally a case study in how to make a horrid, horrible experience on the mobile web.
I already ran to Relay as an escape from Reddit's astonishingly garbage mobile browser experience. Next stop is the door.