Bipedalism evolved (at least) twice and I only know why it happened for Human species

I learned that in our evolutionary lineage bipedalism was selected for for a few reasons including a) freeing up hands for tool use (and by extension mouths for communication), b) raising our eyes above savannah- grass level to better see both predator and prey, and c) reduce surface area exposed to direct sunlight light.

Were these the same reason it evolved millions of years earlier for the dinosaurs/pre-birds that walked on two limbs? The fist and third reason certainly don't apply because there were no tools, languge (probably) and in some cases even usable forelimbs. And I think they stayed pretty horizontal. Which also may invalidate the second reason too.

So, are there theories in what those evolutionary pressures were that lead to bipedalism then?