I'm not sure the sort of athletes that are good at soccer necessarily overlap with the athletes in US popular sports. Most US sports don't require the stamina and foot-eye coordination and probably 12 other things that a good soccer athlete needs. Conversely, I'm not sure Messi has the size for the NFL or NBA and would need totally different motor skills for MLB.
On the other hand, we'd all like to see someone like Kawhi Leonard play goalie.
Ugh. Not sure what you meant by the Leonard comment, but this is the sort of impressions I got from sports enthusiast when I was a kid. (So it's not what you are saying of course, it's what I used to hear from people that irked me). The black players should be goalies if they ever decide to play soccer because that is where they fit best with their *current* skills. Ugh, ugh, ugh! It used to be a well-known thought process that people said black athletes were also not meant to be quarterbacks in football because they were skilled to do other things... plus not having the mental aptitude for that position. Then there was the mindset that blacks could not play hockey because of the wrong skillset... and of course, they could never compete as Olympic swimmers because of skillset as well.
All those attitudes have changed of course, for the better. An athlete is an athlete is an athlete. It's not a pre-disposition of skillset, it's a pre-disposition of passion. There is more passion for a sport, not a lack of skill. Skill is learned but said work is only going to happen if the passion to play a sport at a very high level is there. So what do young athletes in America see most on television? NBA, MLB, NFL and NHL way before they see MLS or anything else. I've seen great basketball players fail at playing volleyball because they don't understand how to apply a skill they already have. For example, it's a different approach to jumping in volleyball than it is in basketball. In volleyball, you take the same approach to jumping as a rebounder does, but you jump up not forward before you strike the ball. In basketball, you jump forward to grab the ball, not strike it. I use the same skillset I used while throwing a baseball that I use to properly strike a volleyball. The arm action, the square of the shoulder, everything is the very same thing... it just needs a translation.
So in short, it's not a lack of athletically gifted players in America, it's a lack of passion to play a game nobody watches and no money can be made unless you are like Pusilic and go to Germany and excel. And I think Messi could do what Altuve did if he had the same passion as Altuve, not the same skillset. Or do what Spud Webb used to do in the NBA.