There’s no thermal limitations on Mac Studio (otherwise, please cite the source). In fact, cooling system is over-designed and Studios remain cool and quiet even under heavy load.
As for Mac Pro, it is what it is. This is not a random decision or lack of technological know-how (just see the tech in their AR glasses, they can design anything they want). Mac Pro is probably 0.1% of all Macs they sell. Out of those 0.1%, some people use specialised pro audio or video capture PCI-E cards and the new model caters for them. And that’s it.
The number of people who need 3D rendering cards in Mac Pro (or actually do 3D on Mac Pro) is probably so small that it amounts to rounding error, there is really no business reason to create separate branch of Apple Silicon processors just for them.
I’m not saying I agree with Apple on this, but as I said, it is what it is.