That is just not true. Merging is so much less work and the branch history clearly indicates when merging has happened.
With rebasing, there could be a million times the branch was rebased and you would have no idea when and where something got broken by hasty conflict resolution.
When conflicts happen, rebasing is equivalent to merging, just at the commit level instead of at branch level, so in the worst case, developers are met with conflict after conflict, which ends up being a confusing mental burden on less experienced devs and certainly a ”trust the process” kind of workflow for experienced ones as well.
Do you know what criss-cross merges are and why they're bad?
The master branch never gets merged, so it is linear. Finding a bug is very simple with bisect. All commits are atomic, so the failing commit clearly shows the bug.
If you want to keep track of what commits belongs to a certain pr, you can still have an empty merge commit at the end of the rebase. Gitlab will add that for you automatically.
The ”hasty conflict resolution ” makes a broken merge waaaay harder to fix than a broken rebase.
And rebasing makes you take care of each conflict one commit at a time, which makes it order by magnitudes easier to get them right, compared to trying to resolve them all in a single merge commit.