What's the purpose of international cup tie? Why adult soccer players can only play for one country? What's the purpose behind that fifa rule? Why can't the rule apply to coaches? Why a coach can manage several international teams, but players can only play for one country?
It's an interesting question. I'm not really sure why a player cannot switch allegiance, although I would think it is just to maintain consistency and prevent it getting to the stupid situation of a player playing for 4 different countries. There has recently been a rule change to state that a player can change his team if he is under 21, and a player can always change as long as he has not played in a competitive game. As for coaches, I have no idea why there is that distinction, other than the fact that they take no part on the pitch, and it is dificult to measure a coaches activity (eg when David Platt managed Sampdoria he was not officially the coach as he did not have his UEFA badges).
In the old days, many European teams will "steal" players from Latin America who are eligible for citizenship.
I believe Veron has an Italian passport as well, could you imagine if he suddenly switched illegiance from Argentina to Italy