I think it's more due to the fact of improving academies and getting football / coaching / tactical periodization taught in college concluding in a general evolution of portuguese football instead of just relying on mid foreign players just because it's cheaper.

Also developing coaches such as José Mourinho, Jorge Jesus, André Villas-Boas, Bruno Lage, Luís Castro, Vítor Pereira, Abel Ferreira, Marco Silva, Sérgio Conceição, Jesualdo Ferreira, Carlos Carvalhal or Leonardo Jardim which consequently led to developing players such as Costinha, Maniche, Tiago, Pepe, Ricardo Carvalho, Moutinho, Meireles, Bosingwa, Nani, Quaresma, Coentrão, Danilo, William, Nelson Semedo, Ruben Dias, Joao Cancelo, Bernardo Silva, Diogo Dalot, Nuno Mendes, Bruno Fernandes, João Palhinha, Ruben Neves, João Félix, Vitinha, Matheus Nunes, Rafael Leão, etc etc etc

I wonder if this had something to do with Portugal's recent success. But I don't think so, it probably was because of Ronaldo, sure.