The person making the change is now going to have to run multiple confusing interactive rebases and git shenanigans, the rewrite the history of the PR branch on every feedback, then you have to re-review all the commits again because they are all different.
It’s possible of course to push all that complexity on the tooling. Have GitHub and git provide tooling for doing all that within the context of a single branch/PR. But why is that better? Multiple branches are easier to manage in git, and as long as they don’t conflict on the merge. Obviously if a feedback on PR#1 causes a conflict in PR#2 which causes a conflict in PR#3 it’s still tedious, but it’s a lot more doable than managing interactive rebases on every feedback comment.