Sometimes you have to get out in front of something to avoid setting a precedent that turns into a problem, one that could have been prevented easier than fixed later.
Other times you can shrug and figure we'll deal with it if it becomes an issue.
Right now Fedor is a net positive. He's not interfering with the tournament or the promoters, and in fact is bringing more attention to them by attending and sharing on social media.
If this turns into an issue down the road with too many others doing the same thing and interfering with tournament scheduling or proprietary streaming rights, it won't be hard to shut it down later. But why worry at this point? Obviously no one is being negatively impacted so anything that helps promote pool and support those playing it can't be too bad.