I think they often use them when they aren't willing to do anything useful, as a "we haven't entirely forgotten that bikes exist, we just don't want to actually

I think they often use them when they aren't willing to do anything useful, as a "we haven't entirely forgotten that bikes exist, we just don't want to actually make things safer" measure (or, more cynically, as a "here we did something now go away" measure). Here in Portland (at least inner Portland) I think they have mostly repurposed them as a bike route marker, where bike route means more or less "a side street that isn't interrupted more frequently than nearby streets" (this being Portland, that is most side streets so there are lots of them all over the place). More heavily trafficed streets are more likely to have bike lanes and green stripes. I think sharrows are resonable as a "this street isn't likely to end abruptly in two blocks" marker, although that is quite a bit different than the initial usage. The city also somtimes installs barriers that allow bike traffic to pass but not car traffic in a few strategic places if a side street is too appealing to cars as an alternative route.