system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: In traffic, why do cyclists by default have to use the road instead of the sidewalk? Aren't motor vehicles and cyclists a bigger danger to each other than cyclists and pedestrians would be?

Doesn't seem reasonable to me from a risk-reward-perspective.

Edit: I wrote this ELI5 from the perspective of a slow cyclist who is intimidated by cars and would feel much safer on the sidewalk. The regulations- and predictability-argument makes a lot of sense - but when I'm driving on a busy street with 15 km/h I feel EXTREMELY uncomfortable with cars (who might otherwise be driving with 50 km/h) lining up behind me (passing a cyclist still requires you to keep your distance, you can't just squeeze by)
gpt
Bicycles and cars are supposed to follow the same rules, and both drivers and riders are responsible for maintaining situational awareness. This is intended to create a predictable flow.

As others have mentioned, while there are notions about how best to walk on a sidewalk, there aren't really any rules or regulations. A bike coming up behind a car can make a fairly accurate assumption about what the car is going to do next based on signals used by the car and/or the lane the car is in. Sidewalks are pure chaos.