Hi Eike,
Actually CDO does depend on Mylyn, and therefore (until 2021-12) on CVS:
EMF CDO depends on EMF Compare's contribution:
org.eclipse.emf.cdo.compare -> org.eclipse.emf.compare
EMF Compare depends on EGit's contribution:
org.eclipse.emf.compare.egit -> org.eclipse.jgit
EGit depends on Mylyn's contribution:
org.eclipse.mylyn.github.feature.feature.group -> org.eclipse.mylyn_feature.feature.group
(Note that despite the name org.eclipse.mylyn.github.feature.feature.group is contributed by EGit to simrel)
The difference is the granularity of the dependencies. For SimRel dependencies are normally handled at the contribution level. At the feature/bundle level there may indeed be no dependencies from CDO -> Mylyn/CVS, but with many contributions being interdependent on each other, and Mylyn historically cutting across so many projects, something that disabled Mylyn causes many things to be easily disabled.
Of course this problem is hindered by Mylyn being under-resourced at the moment.
I hope that helps,
Jonah