Bean counter moment.

So, yes ~$2-3/user/month. The 3p app has to charge the user and then pay reddit. In the case of Apollo, it is to the tune of $20M a year. Apollo (the app) is developed by 1 person and so are most other 3p apps. Suddenly (with months notice) they are going to be billed millions.

Even after the user pays to use a 3p app, they cannot access any NSFW content through it.

This isn't a case of opportunity cost or lost revenue, reddit simply wants 3p apps gone.