Regarding popularity, as was said, much has to do with how accessible a sport is financially, and today, even the availability of the gear needed. Soccer was also invented way back in 1863 in England, well before American Football was in 1920 in the US. There's also the fact that American Football is a far more injury prone sport, with many concerns from parents and schools about children's safety. So naturally children are going to grow up more likely being offered a soccer ball, shin guards, and a simple outfit to play a much more easily facilitated game, with little to no worries of accruing traumatic injuries that can affect them for the rest of their lives.
In fact American Football faced even more criticism after it was discovered that the concussions many got from playing it resulted in extreme pain, loss of cognizance and motor function to a degree, and even suicide. It was studied by a doctor from Africa whom moved to America, and he called the disease CTE (Chronic traumatic encephalopathy}. This resulted in a mass lawsuit against the NFL by wives of players whom died from such trauma, and was made into a movie called Concussion (very good film). This is also why the NFL was forced to change it's gameplay rules drastically to protect players from such injuries, but they can still happen regardless, just not as much.
So, in summary, while events like the World Cup, Super Bowl, and Tour de France, are all massive spectator sports watched all over the world, they differed quite a lot in how many schools carry them, the criticism they face safety wise, and the expense and logistics involved. Even your average racing bicycle anymore is very expensive, with most frames being made out of monocoque (one piece molded) carbon fiber. They also have disc brakes, and many electric or air driven shifters. Hell, even consumer mt. bikes these days are largely made of monocoque carbon fiber, with rear sprocket cassettes that can cost well over $200, vs under $50 when I was doing it.
Don't think for a minute things like this don't heavily skew the popularity of a sport, especially with inflation rocketing sky high. "Mommy, can I play American Style football, our school has it now?", "Wouldn't you rather have a nice pair of running shoes and just get on the track team dear?" Because she's not just thinking of equipment fees the schools charge for such sports, but the possible doctor bills, not to mention the trauma to her beloved son. I used mom instead of dad, because they are the ones fighting most for safer sports, which also cost less. Mom is usually the voice of reason in most households, mine certainly was, but unfortunately she died when I was very young.
When I was very young I clearly remember the day my mom took away my old steel wheeled skate board when she found out we were riding them down a nearby steep street, risking cars running into us at the intersection at the bottom. It certainly didn't help when we told her we had scouts looking out for traffic at the bottom, and were diving into neighbor's trash cans as an emergency brake. I'd literally give up my most valued possessions just to have a mom that cared that much back again. How differently we look at life when we are older and wiser.
As far as soccer having a fair bit of "rest" time, to me, it's more like basketball, you ALWAYS have to be ready for the unexpected, so no real time outs. And it's still one of the sports known most for cramping due to all the running with no water breaks. As far as baseball being our "national" sport, it's another sport that was invented long before American Football, like in 1876. It's almost as old as soccer. It's also more corrupt financially, with no salary caps and even mob influence back when the American Mafia families were at their peak. To many, American Football is the true national sport anymore.
At the end of the day, most true sports fans want a level playing field and no corruption in their sport. American Football certainly isn't void of those problems, but it has a lot less of it than baseball. The Super Bowl gets far more viewers in America than the World Series. It's also hard to justify Soccer getting more viewership than American Football when they are compared on a global scale, because obviously soccer is played in far more countries. I'd really like to see a study done of Soccer's home country viewership where it was invented, England viewership of their biggest soccer game, vs American viewership of the Super Bowl. Or even the country with the most viewers for one soccer game, vs American viewership of the Super bowl. THAT is the only fair way to compare on a national level.
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