Brand has been the subject of a joint investigation by The Times, The Sunday Times and Channel 4 where the claims are backed by a significant amount of evidence vetted by their lawyers. These aren't reckless publications.
These claims have subsequently led to at least some of the involved parties submitting police reports alleging sexual assault. And from reports by the newspapers the expectation is that more parties are coming forward.
This is not trial by TV, social media etc. These are serious claims being taken very seriously because of the strength of the evidence presented to date.
As such, Youtube is absolutely correct here to err on the side of caution.