sure, but an open source UI isn’t going to change that… they’d just close the source!
sure you can fork it, but you can also just copy the UI to an open source clone
imagine if twitter were activitypub: kinda like having an OSS backend with a proprietary front end… i’d bet the move to mastodon would be far quicker… network effects keep people on twitter… same here with OSS backend: we can reimplement the UI and people will have the same experience