I remember projects where out of 50 people only 1-2 were capable and trusted to do merges. And that was a tedious and boring job so the joke was that you never wanted anyone to know you could merge a code base for release.
Arguably git doesn't like it much as well, but it can branch easier.
The real thing needed was the decentralization, CVS/SVN weren't setup to allow every copy to be a master copy on equal footing (and even now most people do NOT use git that way, they setup main or master and let GitHub be the central authority).
It's possible to only commit part of a merge.
It's possible to accidentally include additional changes after a merge.
But I think a more important reason for him was that he felt that CVS and SVN implicitly came with a development model where a small group of people has official commit privileges, while he very strongly wants a model without that.
See for example what he says here: https://www.tag1consulting.com/blog/interview-linus-torvalds... (search for "commit bit").