Well, basically the revolution was done and organized by a group of mid-level army officers. After having succeeded in toppling the government they coalesced into a movement called MFA (translates to Armed Forces Movement). This MFA is essentially where all the political power struggles took place in the following years. Most of the original army officers in the revolution (captains, colonels, majors) were in truth apolitical country boys who had been conscribed to fight a dirty brutal imperial war in Angola, Mozambique etc. which now they were even losing pretty badly (which is why they were motivated to do a revolution in the first place), so they were outmanouvered by the politicians quickly and easily. The more politically-minded people like the one in the pic (Otelo Saraiva de Carvalho) stuck around, but as brave and morally upright as he was, he too was eventually outmanouvered by real politicians in the power struggles.
In the years after the revolution there were two major political parties the Soviet allied Portuguese Communist Party and the Socialist Party (socdemism and even then centrist socdemism). The """""""""""Socialist"""""""""""""" Party was majorly supported by the Germans, particularly as led by Willy Brandt and Helmut Schmidt and the Communist Party was only kinda supported by limpdick Brezhnev, so not much chance of success for the left. This despite the fact that the PCP was by far the most popular and prestigious among the masses because they'd actually resisted the right-wing regime and suffered a lot for their resistance where as the socdems were sitting on the couch just vaguely moaning. Couple all of this with a split from from a supposedly left wing faction of the PCP to form a new meme party (PCTP-MRPP) which was almost certainly infiltrated and controlled by a CIA op back then, to engage in dumb adventurist violence that discredited the left and that's how our revolution was betrayed and disciplined by global capitalism.