> But if their algorithms took the road's capacity into account, everyone would benefit
The people getting extra non-resident traffic on residential streets don't benefit.
But let's ignore them and look only at current drivers. It's quite possible for routing even one car through shortcut neighborhoods to be a net negative, because they have to spend time leaving and merging back with the main traffic flow.
It's not just "roads". There are arterial roads, collector roads, and local roads. Everyone is allowed to use them, but everyone is supposed to use them for their actual purpose. The lowest tier of road is only supposed to be used for the first/last mile of a trip. It is not "efficient" use to pretend all roads are arterial.
The people getting extra non-resident traffic on residential streets don't benefit.
But let's ignore them and look only at current drivers. It's quite possible for routing even one car through shortcut neighborhoods to be a net negative, because they have to spend time leaving and merging back with the main traffic flow.