Yes, in the sense that they're committed to a particular sport. American fans are, for the most part, casual fans of all of their city's clubs across multiple sports. With the exception of a small minority of diehards, it's a matter of "out of sight, out of mind" when the city still has multiple top-tier clubs in other sports. Even in countries where soccer isn't the only major sport, fan interest tends to be in the specific club, and fan allegiance doesn't jump from one sport to an entirely different sport nearly as much as it does in the US. And it's not just the revenue side that's an issue in the US; clubs with similar revenue in the US and Europe are not comparable because even USL Championship clubs have to travel as much as perennial Champions League contenders.