I don't like calling them squatters if you don't know what they're doing and I'm pretty sure you can't actually tell if they're 100% inactive. For example at a time I had zero public activity on bitbucket but was using it for private repos and unlike github this wouldn't show. Then at some point someone kinda demanded I give up the name because I was obviously not using it. Same with Twitter. Just being logged in and reading has huge benefits since they broke the logged-out user experience.

Also archival purposes exist, especially for code repos.