Major Manhattan avenues are thronged with people. Bicycling on the sidewalk is going to be way slower than using the bike lane. Plus sidewalks are bumpier with more obstacles... what cyclist is going to choose the sidewalk?!
I use Citibike all the time in Manhattan. The only bicycles/scooters I see on the sidewalk are the ones pulling up to a building on that block. Everyone else is on the road because it's just faster and easier and safer.
The only blocks where you see cyclists possibly more often on the sidewalk are the handful of cobblestone streets left in the city, which are honestly just murder to bike over. Or a certain small number of roads that function more like highways where cycling in the road is unsafe period.
Edit: I am abandoning this account. I was downvoted below for refusing to specify where I live. This community is not worth being a part of.
Note that kids under a certain age are allowed to bike on the sidewalk.
I made the same decision years ago at University. I'd much rather risk a ticket or minor pedestrian accident by riding on the sidewalk than risk my life comingling with cars who don't give a shit.
The notion that New Yorkers use bike lanes is funny. I live on a major Manhattan avenue with a bike lane and there is at least three times as much bicycle traffic on the sidewalk right next to it. Even motorized scooters are more commonly seen on sidewalks than the road. When I lived in Brooklyn I learned to peek my head around the corners of pedestrian bridges because motorists and cyclists will speed around them recklessly. The food delivery gig industry has put this behavior into high gear. It’s illegal, but New York laws are more like guidelines.
From my fire escape I can see a vacant lot that is used to store stolen bicycles while they are advertised on craigslist. I guess I wouldn’t have to go far if I decided to buy a bike.