They would instead rather charge far more money for data access for things like AI training etc, Twitter have also made similar changes to their own API to prioritize high bills for AI training use cases, not third party clients. That's at least how I see this change. The high pricing for these customers also removes the need to worry about the ad tech situation as is the case in the third party clients - you can just offer them an ad free feed at these prices for the training requirements.
I suspect the internal at Reddit desire to have less third party clients may well predate the AI discussion too, given almost all companies in this position eventually want to wind down those clients as history has shown again and again, for all of the reasons discussed in this thread.