They're running on custom ASICs as far as I understand, it may not be possible to run them effectively at lower clock speeds. That and/or the market for it doesn't exist in the volume required to be profitable. OpenAI has been aggressively slashing its token costs, not to mention all the free inference offerings you can take advantage of

It's a lot more expensive than normal, $2.25/2.75 I think. Though their subscription is a lot cheaper.