Visa for this cases isn't a big problem because Companies like Riot Games could arrange this stuff easily and quick since they are a trusted and Big Company. It's obviously because of Covid Risk. I mean it's not a Visa for Vacation. It's a Business Visa i would call it and this kind of Visa is not that hard to get, even if youre from the Philippines. But im not an expert in this cases. If it's really because of just Visa, it's a shame.
Signed Pro Gamers who attend International Events with known Orgs should never have to ask for a permission to enter any Country if it's for an Event and a short time.