There are already concerts with paid tickets going on in platforms like Fortnite, that just happen to be able to act as multi-user VR environments, even though that wasn't their designed purpose. The demand is real.
I don't see it as much of a bet that "people are already creating these events, and want to build professional services around doing so; these people would appreciate a platform to run such events on that won't be shut down/go unmaintained in two years just because the game that the platform was built for ceases to be relevant; and people who pay to attend these events are willing to download a client to consume the content they paid for." That just seems to be a series of common-sense facts to me.
Whether Facebook can actually end up as the platform of choice for hosting said events is entirely non-obvious. But, if nothing else, they do have connections, channel partners, global scale to deploy reliable infrastructure that can be trusted to not buckle under event load, etc. It's up in the air how much things like "the aesthetics of the experience" really matter, compared to those. How much does a band care about the aesthetics of the venue?