After the carnation revolution when the people where fed up with the colonial wars portugal went through the "PREC" (Processo Revolucionário Em Curso) which was a short era of societal reform that included nationalization of companies, the collectivization of farmland and the general growing of popularity of various worker-movements/ parties like the PCP (MLs) the PCTP (Maoists) and others like the UDP and some trots but nobody really gave a shit about them. It was a period of unlimited potential for a revolution and yet it failed to establish socialism in the country. From what i can tell, the main problems were disorganization within the parties themselves (especially the PCP which was the largest communist party and could've done much better than this) and the restraint to overthrow the state by violence. The PCP, one of, if not the, leading leftist party of this period refused to establish dominance by violent means...they know that the only way to establish a socialist government is with a revolution yet they seemed so paralysed during this time. On the 25 November of 1975, communits and socialists unsatisfied with the more "soccdem" way Portugal would take, decided to start a coup but failed as armed "moderates" stopped the attempt before it having any effect. Since then Portugal is just another european "soccdem (nuts)" country with a Neo-liberal government. The PCP still has seat in the portuguese parlament but is loosing relevance more and more while the "CHEGA" (a quasi fascist party with anti-immigration plans and tax cuts for rich and whatnot) party is gaining more popularity. Portugal could've become "europe's cuba" as Otelo Saraiva, a portuguese revolutionary put it. But at the end, fell victim to your average reddit-style "enlightened centrist" who wants a welfare system while conserving the neo-liberal mechanis.
Everything was going well until the US put the CIA to work. They organized a front against the communists. Mário Soares, who was the face of this movement, was very popular. He was the leader of the Socialist party, a fake leftist party that claimed to want Socialist reforms, but with moderation. There were still sectors of the military which were fascist. The Communist party had several buildings bombed during the counter movement. During this time, a massive anti-communist propaganda campaign was launched against the Party, even accusing the leader of "eating children for breakfast".
The communists simply didn't have the numbers, military equipment or training to fight a civil war. And quite frankly by then, they had already lost a good amount of popular support. So this Social Democratic system was what we got as a result of the balance of powers. The workers right have been eroded over time and Portugal is just a STEM factory for the Nordic countries.
Let's get one thing clear because I see this confusion appearing over and over again. The PCTP was not communist, nor Maoist, not even leftist. It was just a fake communist party created to bash the real communists. That's all they've ever done. The UDP were just a bunch of ultras that never accomplished anything, but they still exist for some reason.