Posting here as person, not as Riot employee - I don't do anything in esports so I have no power to effect change here:
I recently got my US work visa. I originally was approved by the USCIS in December for work, 2 weeks after applying, but it took 2 months to get a visa interview and another 6 months after that to go through the hoops.
It's very difficult to get a US visa even if you tick all the requirements, like I did.
For temporary student or work visas, it's even harder, because they are non-immigrant single intent visas; you have to prove you have the funds to support yourself in the US and prove that you intend to return home, which can be quite difficult and is objectively subjective.
Plenty of countries need immigration reform but it's next to impossible to enter the US for work these days, even if you don't want to immigrate, even with good immigration lawyers