Pinboard is still quite active. If you need proof just go to /recent which is a live firehose and interesting to see what people are bookmarking. I use Pinboard and regularly export my bookmarks incase their servers are hacked/wiped/corrupted.
Part of it is also that tech bros are upset that Maciej didn't go full-coinbase and is instead pretty active socially/politically.
I'm happy to keep using it and paying for it. Works fine for my needs.
I pay to keep the servers running, not so I can have something new and shiny every month. If it somehow quits doing what pinboard does, then I'll look at alternatives.
I was using Magnolia before Pinboard and it went down permanently. Fortunately, at the time, I was doing link blog posts once or twice a week so I was able to recover most of my links with a bit of work.