OpenAI played stupid games, won stupid prizes. They have designed a subscription where the optimal behaviour is to spend down limits as soon as possible, because if you don't their random resets, which make up almost half the value of subscriptions sometimes, will be wasted.

But to do THAT you need to max out every 5 hour block. Of course people are going to start abusing unlimited chat in the mean time and start optimising the ability to burn tokens as fast as they can.

It would be easy enough for OpenAI to block this kind of use, both in their TOS and technically. It seems like there would be plenty of other reasons not to support unlimited chats long term.