The problem with American cities is that we only have two spaces: the road and the sidewalk. Bike lanes are sometimes added to roads, but they're still just lanes on the road. The roads have all been built and designed for cars. Sidewalks have been built for pedestrians. Bikes, scooters, skateboards, etc. just don't fit well into either space.
There's a great YouTube channel, BicycleDutch [1], that goes into some detail about the Dutch approach to thoroughfares. They almost always build three spaces: a road for cars, a path for bicycles, and a sidewalk for pedestrians. This results in a huge number of people using bicycles to get around; in Amsterdam 30% of people always commute with a bicycle and over 40% usually do.
Of course, it generally wouldn't be practical for an American city to just convert all its roads to also include a separated bike path. Instead they could look for areas where a bike path could be built without costing too much, drawing political ire, or significantly interfering with current use. Railroad tracks are good opportunities. As an example, Minneapolis converted an unused railroad corridor to a separated bike path, called the Midtown Greenway [2]. As of 2016 34,000+ people used it daily [3]. Portland, OR, has converted two former railways into bike paths, the Springwater Corridor trail [4] and the new Trolley Trail [5]. We have plenty of other separated paths here as well.
Where there just isn't enough horizontal space, a more radical approach would be to build an elevated bike path over a few major thoroughfares (i.e. main downtown streets) or freeways that connect commuters to other separated or multi-use paths. Xiamen, China, built an elevated cycle path -- really more of a bicycle highway -- last year [6]. Dallas [7], Phoenix [8], and Detroit [9] have all built parks over freeways that contain some mixed-use paths, though not always with transportation in mind.
Ultimately bicycles/scooters/etc. don't really fit well into the current American infrastructure, but it seems like a solvable problem.
1: https://www.youtube.com/channel/UC67YlPrRvsO117gFDM7UePg
2: https://en.wikipedia.org/wiki/Midtown_Greenway
3: http://www.minneapolismn.gov/www/groups/public/@publicworks/...
4: https://en.wikipedia.org/wiki/Springwater_Corridor
5: https://ncprd.com/parks/trolley-trail
6: https://www.mnn.com/green-tech/transportation/blogs/china-cy...
7: https://en.wikipedia.org/wiki/Klyde_Warren_Park
8: https://en.wikipedia.org/wiki/Margaret_T._Hance_Park
9: https://en.wikipedia.org/wiki/Interstate_696