Oslo, Norway was so clogged up by electric kick scooters they had to pass an ordinance to heavily restrict the number. Bikes and scooters are viable as a means to reduce car traffic plenty of places. They can't be the only means of transport, because yes there are people who can't use them, but they can be a significant mode of transport even in far colder places than California. Oslo isn't very hilly, but it's also not flat, and electric bikes and scooters can compensate for a lot of (not all) physical ability challenges.
