The hot pass isn't really that hot when you are tig welding a pipe weld. The term hot pass probably came from stick welding pipe with 6010 where you run the second pass pretty hot to burn out any slag left over from the root pass.
For pipe welds that are tig welded, the second pass is often done at the same amperage as the root....and the goal is to put in a good root pass and then not screw it up with the hot pass.
After the hot pass is in, its less likely you will mess anything up.
Some pipe welding tests are tig welded all the way out. But some are combo welds with tig root and hot pass but stick welded the rest of the way.