I don't agree with this. Getting a visa for Mexico or Canada may not be a big deal for US/EU citizens. But if someone from China or India want to visit these countries, in order to watch the world cup matches, they still need to go through a lot of formalities. And getting a US visa is entirely at another level. For people from the third world, it is next to impossible to get a tourist visa to the US. In short, I guess the fans will be mostly comprised of EU/US citizens for the 2026 event. Very few of those from Asia or Africa are likely to travel in order to watch the matches.
Yes, the US is already expecting a lot of tourists application because of the upcoming World Cup and they already know that people from 3rd world countries are already applying at a much earlier phase because the people are also expecting that it will be not that easy to get a visa to fly and step foot in any US soil and they know as well that it will take a few couple of months before they can have a schedule.
I think it's already agreeable that people from EU and first world countries will not have that much struggle just to secure a visa because having a passport is already a perk and some of the countries don't even need a tourist visa to visit US, Canada and Mexico.