Would a child or elderly person feel comfortable on such a lane? Generally, no. They're not accessible, and generally a waste of space.
It's largely municipalities cheaping out on infrastructure, because outside of, say, the Netherlands, biking is a second class citizen at best, and often more like third class.
Fair though, a painted bike lane is probably better than nothing.
> even in most of the EU
Why are you saying this like the EU is some kind of exemplar? Most of the EU sucks for biking. It's better on average than the US, but most countries there aren't like the Netherlands, which is probably the only country there where biking is treated with similar seriousness to driving in terms of investment.
That gives me an idea of what minimum infrastructure and driver behaviour is required for ordinary people to cycle. And in spite of your preference for 100% separated infrastructure, that doesn’t seem obligatory and I don’t think it crosses any of my neighbours’ minds.