There is a reality that when they control the client it can be significantly cheaper for them to run: the Claude code creator has mentioned that the client was carefully designed to maximise prompt caching. If you use a different client, your usage patterns can be different and it may cost them significantly more to serve you.

This isn't a sudden change, either: they were always up-front that subscriptions are for their own clients/apps, and API is for external clients. They don't document the internal client API/auth (people extracted it).

I think a more valid complaint might be "The API costs too much" if you prefer alternative clients. But all providers are quite short on compute at the moment from what I hear, and they're likely prioritising what they subsidise.