I'd argue it's more to do with the youth academy system in any country than a league the players barely ever played in.
If the Portuguese league was so strong, why has it been so long since Sporting, Benfica or Porto made any impact in Europe?
It's no stronger than the French league. A country that has won considerably more at international level than Portugal.
Portugals last international fixture saw a starting 11 of
GK - Roma
LB- PSG
CB - PSG
CB - Real Madrid
RB - Man City
Mid - Man United
Mid - Wolves
Mid - Porto
Forward - Milan
Forward - RBL
Forward - Everton
ONE player for the national team in the domestic league. ONE!