That a broad generalization based only on your specific experience.
Chicago, for example, continues to build bicycle lanes separated by concrete medians, bollards, and in the case of the big new developments in the South Loop, bike lanes separated from traffic and sidewalks by trees.
The biggest downside to cycling in Chicago is the winter. Not just the cold and wind, but the fact that snow from the sidewalks is often shoveled into the bike lane.
I'm sure there are other American cities doing the same thing.
I think the one advantage unprotected bike lanes have is that they're easier to maintain. Re-paving is simplified. And you don't have to invest in tiny bike lane snowplows.
In Austin, I basically refuse to use the two most significant protected bike lanes near where I live and work because drivers far too frequently turn into the lanes at intersections without looking. The city put signs up telling drivers to look and yield at some intersections, but the signs don't seem to have had any effect other than covering the ass of the city.
Well built infrastructure would be preferred. But ultimately we need more than just infrastructure. Drivers need to change their dangerous behavior too.
And unfortunately this likely won't happen. Despite a large coalition of biking advocates in SF, the SFMTA won't lift a finger. It's a corrupt, incompetent organizations that won't green light anything other than useless pork projects. And once the moneys in...the execution is irrelevant to them. Just look at the Van Ness BRT, Central Subway, Transbay Center construction.