For enterprise usage bitbucket is currently not so much suited. A repository has contributors, and all of these contributors are automatically added to a pull request, for approval. This is impractical as it sends an email to all. It is slow if there are many contributors. If one wants to remove some it is slow as well and pointless work. usally one needs a couple of. Just like done in GitLab, or GitHub.
Is there an easy way to change it? if it is switched off to pre-populate than everybody can be entered to be an approver, no relation to this repository necessary. That causes other headaches in enterprise contexts. audit issues for example.