Why MR train merge only first MR

Currently we have an issue with dependabot. to automatically update dependencies in package.json dependabot create automatic MRs per dependency
Let’s assume dependabot created a 3 MRs, I cannot merge them one by one, as after the first one I need to rebase the other 2 and wait for their pipelines to run - which is slow

So I thought MR train can help me, but when I start release train for the first MR and add 2 other MRs (with green pipelines) to MR train,
gitlab launches a few pipelines but really merges only the first MR (which I can merge even without MR train)

Am I doing something wrong or just don’t understand what MR train is?
Is there a way to merge 3 MRs without rebasing other two?