It might not stop them, but chances are pretty high that if they launch their own coin it'd end up like Diem coin. Creating an altcoin isn't the problem, but the thing is that they usually do not have any actual use case and survive only on hype, once the hype is gone, the coin is gone too. I would not bet on any social media app succeeding if they launch their own coin, it would survive for sometime, but i am pretty sure it'd not last long, there are already enough altcoins copying one another but solving no problems.