I think we need to wait for Larian to implement multiattack for player characters. Because I feel like they put shove as a bonus action to resolve "replace attack with a shove" in an easy way, as well as to help martial classes early on, as others mentioned.
If we get an "attack currency" then that should be used for shoving, as in 5e. Otherwise, I would prefer it to be an bonus action rather than have martial classes sacrifice all of their damage to shove an enemy.
