Points to consider

1. Perhaps the PL is a bad example, but about half the managers are from the UK (and not all are from England itself). The managers of the top clubs, presumably the best managers, are mostly from foreign countries. Does the home-grown manager give the best chance of success.

2. Managers from within the country may have or perceived to have their own favorites from their own team and may have a bad history with players. An outsider may have a cleaner path to selecting the team.

3. For less-accomplished nations (e.g. the USA) the level of play in hte national leagues may be inferior, and a home-grown manager may not realize how his choices stack up against true world-class players.

4. The MLS-syndrome is probably not unique to the USA. An outsider has his own best interests at stake and is not burdened by the financial desires of the home country that often work against development and/or selection of the team.