Generally disillusionment with communism combined with an eye for their pocketbook. It's the same journey a lot of the neocon crowd in the US made.

Barroso was a Maoist at his university before the revolution, but right-wing ever since. It's just that in Portugal, going with the public mood after the collapse of fascism (we often forget that fascism didn't end with WWII on the Iberian peninsula, just grew sclerotic), right-wingers from the pro-democracy-reformist 'liberal wing' of the ancien regime named their formation Social Democratic Party. But it is a right-wing party like any other, the centre-left party (which won the elections after Barroso's departure to Brussels) is called Socialist Party.

_{*Lunatic*, n.
One whose delusions are out of fashion.}