Notice it says "APP" mode, not "LOC" mode, although logically the implications would be the same for the LOC mode.
I would argue the reason there’s a difference is if LOC captures the wrong localiser, you can engage another roll mode and recover.
If using APP and it locks onto the wrong ILS, you’d have to select TOGA or turn off the A/P and F/Ds and then rebuild, all while turning the wrong way, possibly towards hills. Bit messy.