Bikes are considered vehicles by law & must follow traffic laws & stay off the sidewalk. On many roads, bikes can travel @ 50% or greater of the speed limit. It is unsafe for a bike to travel @ 15-20mph on a 3' wide slab of concrete & approach a pedestrian (or 4) with no room to pass. The car always has a few feet they can move over to clear the bike. Plus getting off the bike @ every intersection (as a cyclist is supposed to do, if on the sidewalk -with kids) would defeat the purpose of riding.
Pedestrians or joggers, especially when there isn't a sidewalk are supposed to walk against traffic.
The reason is:
A) they're hardly moving relative to traffic, so for the car it doesn't matter
B) it allows the pedestrian to see oncoming vehicle and have a chance to dodge it if the driver veers towards them.