I believe they wont for the same reason they wont have more than 3 active items. Controller players are too limited with their buttons. Its simply not enough buttons for more stuff. Sure, you could do something weird like "L3+R3 is jump" but that would be so clunky and technically be a disadvantage over KBM and they want to make it as even as possible.
Definitely sucks since id like it aswell, but i dont think it will happen
Not giving an OPTION to do it to users is silly and will lead to minor negative player perception of the mechanic in the long term, especially as they add more functionality to it.
Jumping is not a game essential mechanic, so if they allowed everyone to rebind it to something else, like L3+R3 as you said, it wouldn't actually affect their performance.