The biggest venues in the United States were designed around American football and concerts, not around the surface international soccer requires. Preparing one to host a match is a construction project.
International soccer is played on grass
The governing standard for major international competition is natural turf, and artificial surfaces used routinely in American stadiums do not satisfy it.
The reason is partly how the ball behaves and partly injury risk, since the ball skids differently and the surface offers less give when a player slides.
A stadium that plays its regular season on synthetic turf therefore has to install a grass field temporarily, then remove it afterward.
Growing the field happens off site
Turf for these installations is typically grown elsewhere in conditions matched to the venue, sometimes for many months before it is needed.
It arrives in trays or rolls, is laid over a prepared base inside the stadium, and is given time to knit together so it does not tear under load.
Agronomists then manage light, water and root depth in a bowl that was never designed for growing anything, which is why roofed venues need supplemental lighting rigs.
The field dimensions are the other problem
A soccer field is wider than the space an American football stadium naturally provides between its lower seating bowls.
Meeting the required width often means removing rows of seats, relocating team benches and camera positions, and rebuilding the sideline area entirely.
These changes reduce capacity in the most expensive part of the building, which is one reason the work is expensive well before any grass is bought.
Climate makes the same job different in each city
Grass species that thrive in the northern part of the country struggle in southern heat, and the reverse is also true.
Host venues in hot regions often need cool-season grass to satisfy the standard, then have to keep it alive through conditions it did not evolve for.
Indoor and shaded stadiums add another layer, because turf grown outside has to survive being moved into a building with limited natural light.
Why the work is worth doing anyway
American stadiums offer capacity and infrastructure that few venues anywhere can match, and that advantage outweighs the surface problem for tournament organizers.
Organizers also gain a venue with parking, transit links and broadcast facilities already in place, which removes the temporary construction that smaller stadiums elsewhere would require.
The result is a familiar pattern where a building that looks unchanged on television has been substantially rebuilt from the field up, then quietly returned to its regular configuration once the tournament moves on.