The number of issues is much more an indicator of how issues are managed than anything to do with the quality of a project. Some projects prefer a small number of larger issues, others a large number of small issues. Some have bots that close issues after inactivity regardless of whether they’re still valid, others have a large number of inherited issues.
The Sublime Text issue tracker only recently became official, before which it was managed primarily by community members. The vast majority of issues simply have never been looked at by anyone on the team. If you instead look at the pulse statistics you can see the number of issues is trending downwards: https://github.com/sublimehq/sublime_text/pulse/monthly