Better explanation:
Cant place torches on the side of path_blocks

They have flat sides? Whats the issue here?

1.15.2 mechanics: Wont place on the side but will force it onto the ground. 
1.16.1 mechanics: Wont place at all/will place on the block beside it.

My outcome: Why cant we place torches on path_blocks? They lose barely any texture to become a path and the torch can clearly still have a grip on the side of it?

You can place torches on the side of soulsand and they step down when you walk onto them?