User blog comment:MisterWoodhouse/Introducing the Fandom Wiki Managers and Content Team/@comment-30625039-20190527202552/@comment-24006128-20190528144403

All skins, including at Wikipedia, had to be updated with new processes in order to be GDPR compliant. The differences between Oasis and Monobook were so significant that they would need separate processes to ensure compliance. Building and maintaining two separate processes was not an effective use of developer resources, so the difficult decision to remove Monobook was made.