@WilliamGunn He is very chummy with the head of FIFA and even attended the significantly lesser-known Club World Cup final. He came down onto the field to hand out all of the winners and losers medals and photobombed the winners' trophy celebration.
Trump loves the spotlight, and for context, the last Superbowl reached 191M people. The 2022 World Cup Final reached 1.5 Billion.

@WilliamGunn As a US soccer fan, I have spent more time than I'm willing to admit having to wrap my head around Trump's relationship to soccer.
At it's core, I think he just loves a crowd. If he could insert himself into the NBA Finals or Superbowl more, I think he would. (Okay NBA Finals, the boos might be too much).
The real surprise is how the FIFA president managed to convince Trump that this summer's US-based semi-experimental Club World Cup was worth attending. Though, I suppose one look at the trophy could explain it:

See also: Trump says Club World Cup trophy will remain in Oval Office after tournament’s end | Club World Cup 2025 | The Guardian
I actually think soccer's diminished popularity makes it easier for Trump to insert himself. For the most part, the powers that be have kept him from inserting himself too deeply into the more traditional American sports, but since no one cares about soccer in the US*, he has a lot more leeway to do whatever he wants.
I am very excited that the US is hosting the 2026 World Cup, but it will be bittersweet if Trump finds a way to make it about him.