It isn't obviously complete either, and definitely still has bugs. And there are significant changes on master that haven't made it into a release yet. I think it is more that the maintainer(s) no longer have a lot of time to put into it. Which is fine and understandable. Maybe eventually a fork will gain enough traction to take over, or maybe one of the alternatives will become more popular, or maybe the maintainer will come back, or pass it on to someone else.
Though it's funny because I do agree that in the past that jq wasn't having its committed code being released often enough. There was a popular Github issue[1] with arguments and 70+ reactions about a confusing feature in jq that turned out to have already been fixed and committed in 2015, before the Github issue was even opened, but the fix didn't actually make it into a released version until 2018. Definitely one of the more frustrating cases of investigating a software issue I ran into. Everyone should make sure their project's release process can promptly release updates!
[1] https://github.com/stedolan/jq/issues/1110