Agree that is annoying, but if you start excluding such results then how does one find that type of content?
You clearly label paywalled content with a symbol or image.
I think the only issue there might be that google might be unaware that it is a paywalled content due to how many sites allow crawlers access to content but not to users (based on crawler ip ranges). Agree such a flag would save time when available or even a search filter option to skip those results.