Football (soccer) developed into its modern form in the 19th century. At that point, countless European immigrants had - of course - already settled in Northern America. Still, when football had arguably already become the most popular sport in Europe (late 19th and early to mid 20th century), hordes of Europeans - including many Italian, Irish, German and certainly after WOII Dutch people - moved to the United States of America and Canada in order to start a new life. Yet, football (soccer) has arguably only gained significant popularity in both USA and Canada over the last few decades. Why is that?
Many, many thanks in advance!
OK, I'm going to preface this answer by saying this: this question triggered a memory in me from some years ago on a National Public Radio interview discussing this exact topic. I then (at the time) went and found the book in question and looked it over some, but did not read it cover to cover, and it's been a while since I did so. However, the ideas and arguments were not difficult to remember.
Michael Mandelbaum in his book The Meaning of Sports: Why Americans Watch Baseball, Football and Basketball and What They See When They Do posits that the answer is because basketball became the game of choice instead. And he's got some good points on his side.
For one, you can drive through rural America (specifically the United States) and you will pass by any number of homes with some form of basketball hoop/goal in their driveway. While you need the goal/hoop, you don't need much room for a half-court setup, whereas you need more space for even small pickup soccer. Basketball hoops are sometimes placed inside barns (which is where the term "barn ball" to refer to a pickup game with very few rules comes from).
Basically, basketball is the pickup game of choice in rural America and also in the inner cities because it takes less space to play, and he also notes that at various points in American history soccer's association with Europe has on its own made it a difficult "sell" to Americans, as "European" or "Euro" are often used as pejoratives in the United States.
He also discussed that a number of elite NBA players were also very good soccer players in their youth, but obviously chose basketball instead. In the U.S., the best athletes almost never choose soccer over the other sports, and so it's then a self-feeding cycle.
Other minor points include that Americans hate draws/ties. Draws are a regular part of soccer though, and that can make it to a tough sell to very competitive Americans that like a binary winner-loser setup.
The TL;DR: Basketball is a ball/goal sport. Soccer is a ball/goal sport. One arguably takes less space to play, and now that it's so entrenched it is extremely difficult for the United States to produce enough elite/top-end soccer players to really capture the national attention and swing it more in soccer's favor.