Serious question, why auto switching is a something that anybody may want ? I want to change weapon when i cannot use it.
Iirc, we had auto-switching-on-empty in Titanfall1 and Titanfall2 (though you mostly *couldn't* run out of ammo in Titanfall2-MP, so was a non-issue). So it's just something that didn't come up much before, and was the right call for Titanfall2-SP, and carried forward without much examination.
If the game wasn't out yet, I suspect we'd push for this (not auto-switching) as the default, instead of the other way around.