Extremly popular, as the matter of fact - soccer is the hottest tv market by growth ... there is nothing but money in soccer !!!
Yeah soccer is definitely popular in the US (far more so than tennis of course) as basically proven by a whole host of metrics and stats. It's just that it's one of many popular sports in a very crowded US market, so it's lower down the rankings there compared to many other countries. The US men's team have a lot of exciting young players doing well at clubs in the top European leagues, and they could be primed to do well at the 2026 World Cup on home soil (75% of the matches will take place in the US).
On a side note, sometimes here and sometimes in other outlets / places, I have noticed that some of the same people who think that men's tennis is absolutely thriving nowadays and that things will be perfectly fine after the big 3 have all retired, spend nearly all of their tennis discussion energy on big 3 related topics and GOAT discussions. Surely if they enjoyed the current state of the sport so much and thought that it was in such safe hands post-big 3, they'd find more time to discuss and take an interest in a wider range of players? That includes guys I know in person who think that men's tennis is better than ever nowadays (which I personally find laughable but we're all entitled to our opinions), but weren't really interested in the US Open, YEC and Miami finals sans-big 3 members during the past 7 months.
From my perspective, I certainly do not think think that men's tennis is absolutely thriving nowadays given the weakness of LostGen and ever shrinking variety in playing styles (it's certainly not an anti big 3 thing, I thought it was in a much better state in previous eras including when each of them enjoyed remarkably dominant seasons, but crucially when players born in the early and / or late 80s were largely in their primes), or that things will be perfectly fine after the big 3 have all retired. I'm deeply concerned.