Mastodon and other federated platforms are still confusing to normies and less ideologically-minded users. Aside from that, unless VLC starts hosting their own instance, it is hard to say if the particular one they decide to use will stick around. They can relocate by taking some extra steps of course. But they would likely care to put that effort into making VLC Player better instead of into social media. For now at least. X has been more or less the same for a long time (even with the past couple of years) for what they use it for. I am sure they would like to be on an open platform over propriety if that were the only difference. And nothing is stopping them from using both at the same time in order to reach as many people as possible.