That was my first thought as well, then I realise CVS is not maintained for more then a decade. I know not everyone likes Git but wouldn't SVN be a better solution.
Have you considered CVS may have been finished for over a decade? OpenBSD has been using it for a long time, and it clearly meets their needs, or they'd chose from one of the many other choices.
In my own experience, it's nice to use finished software, step off of the upgrade treadmill, and get to the end of the learning curve.
Feature bloat, totally agree. But even for bug fixes and performance improvements, I have a hard time believing this is truly finished.
Based on the timeline of CVS, I doubt there are that many large performance issues that can be fixed without significant risk of breaking. In my experience, CVS was primarily limited by network and disk I/O, both if which ate generally much improved since the time of active CVS development.
Keep in mind that the effective scope of CVS is also shrinking as many users move on to other software; that means any issues are less likely to surface.
https://cvsweb.openbsd.org/cgi-bin/cvsweb/src/usr.bin/cvs/
It's not especially active, but you can see the last change sets were in the past year, so "not maintained for more than a decade" doesn't apply to what they're using.
The CVS that OpenBSD uses is still GNU CVS - https://cvsweb.openbsd.org/cgi-bin/cvsweb/src/gnu/usr.bin/cv...
I thought I remembered -current moving to opencvs some time ago, but either I mis-remembered or they moved back.