or Mexicans playing in MLS? Mexican clubs play really well. Why haven't more of them tried to chase the likes of Dempsey or Donovan at their prime? Or other young US talent? Or perhaps Americans returning from Europe, is Mexico slightly interested in some? and of Mexicans players surely some playing in 2nd or 3rd division in Mexico might wanna try their luck in MLS?
Because there is a cap on foreign players and they prefer to pickup a proven South American player which most likely would be A) a better player B) a cheaper player.
That level talent hasn't proven to be any better than the domestic talent in the USA. There are no foreign player restrictions in the USA, so if there were gobs of high-level, less expensive talent in Mexico, MLS would be chasing it. It's just not there - the talent good enough to play in MLS is also good enough to play in MFL, where the lower end teams can still pay better than MLS.
Yes, MLS (and all USSF sanctioned leagues) has foreign player limits. There are 8 slots per club for foreign players and these slots can be traded.
a proven SA player is cheaper then a US talent? It still confuses me that we don't have a fair number of US players in Mexico for the past few decades and a large amount of Mexicans in MLS, especially now.
Proven meaning that they did well in their domestic league then most likely they will do good in the Mexican league. A proven American in the MLS does not mean they can do good in the Mexican league, lets be honest here the MLS is not up to par.
Both LMX and MLS are leagues that will pay local players a fair bit more than their actual talent warrants in the international market. MLS will occasionally splurge on a Mexican player but it needs to be a marketable one. Cuah, Gio, etc.