The reasoning behind this is because complex rigs use empties and control objects as well as armatures, Add Constraints (With targets) shouldn't only be available on pose mode, it is an object operator as well.

Riggers are the ones who have to deal with adding hundreds of constraints to a project and it's an exhaustively repetitive task, the best tool we have so far for speeding up this process is the Add Constraints (With targets) menu.

Since It's an extreme time saver, the better option is to have it enabled on object mode too, for sake of rigger's patience.

If the shortcut got removed because of the minimal keymap, remember that the Repeat Last removal wasn't a good idea either, the same here.