I don't either but since MLS has been established only Klinsman hasn't been. The next cycle it may work the other way especially as it seems possible almost all of our players are in Europe. Then it could very well be deemed that a coach with high level European experience would be a better fit.
It's a trend that predates the MLS. Of all the head coaches the USMNT has ever had, only 3 were hired without prior experience coaching in the USA: Klinsmann, Milutinovic, and Dettmar Cramer. Cramer was head coach for all of 2 games in 1974, and Klinsmann had been living in California since 1998 when he was hired. Milutinovic was the only long-term hire with no personal American connection in US history, and that was considered a radical departure at the time. It's not an MLS thing. USSF just prefers coaches that it feels have a tangible "American" connection. In any case, I didn't just mean that Berhalter was inexperienced as an international coach (though of course, he is). But generally speaking, he's a young coach, and he hasn't really been in many high-pressure situations before. The closest was the 2015 MLS Cup. I would even venture to say that the Gold Cup final vs Mexico is probably the biggest match Berhalter has ever coached. And I think he made a couple less-than-great decisions as a result.
Scuffed podcast talked about how there was a rumor that Boyd picked up a hamstring issue which is why Berhalter didn't select him late in the tournament.