Assuming we're not talking about the extra-wide sidewalks common in city centers which sometimes also host designated bike lanes, ordinary sidewalks that I've seen throughout the US and Europe are nowhere near wide enough to fit even a single cyclist passing alongside a pedestrian without a risk of collision. Add multiple pedestrians walking alongside each other, other hazards such as parked cars, less competent cyclists such as children, or pets (on or off leashes) and it quickly becomes a recipe for disaster for one or both of the sidewalk users.

Also, bicyclists in cities tend to travel closer to the speeds of cars than pedestrians, and tend to have more similar dynamics such as turning radius and stopping distance which infrastructure for cars is already designed around. Additionally, car drivers are licensed and there is an expectation of awareness that they must exhibit. This makes it far easier to place slower-moving "hazards" in their path than adding faster-moving vehicles in the path of pedestrians.

On top of everything else mentioned in the sibling comments, riding on the sidewalk is illegal in many locales.

https://www.sallymorinlaw.com/bicycle-accidents/riding-your-...

The most dangerous part of a sidewalk for a cyclist are places where they intersect roads. Drivers just aren't expecting sidewalk users moving at bike speeds.

Some areas have long stretches of sidewalk without intersections those are fine for cycling assuming they have little pedestrian traffic or are wide enough to pass safely.

Cars and bikes mix better than bikes and walkers. Which is to say not very well. Walkers move in unpredictable ways and freeze when a bike is heading at them. Bikes move more like cars - they get a bit better handling, and are not as fast, but overall they act like cars.

I wouldn't want to bike when there are many cars in the same lane as me, but it is still safer than biking on sidewalks where are many pedestrians.

* It's illegal in most countries

* It tends to be busy with pedestrians (not everywhere, as you mention)

* It's not safe when crossing side-roads

* It's inefficient if you walk at junctions

Riding on the sidewalk is dangerous. Cars do not look for you when moving between the street and a parking lot/driveway/etc.

I have had more close calls with cars riding on at most 10 miles of sidewalk (and that's being generous to be honest) in the past decade than with ~6000mi riding in the road.

In some places it is illegal to ride on the sidewalk.

Also, the width and amount of obstructions on sidewalks varies widely.

You should try it?

Depends how walkable the city is.The more walkable it is the more people you will see on the sidewalk.Sidewalks are for pedestrians not for fast moving vehicles.

You know how many in the cycling movement view automobiles as being fast, dangerous, machines clogging up the roads? Many pedestrians view cyclists as a similar fast, dangerous (often rude and inconsiderate) presence on the sidewalk.