The concessions obtained through SocDem goverments in European countries came about because all those countries had thousands of actual communists in varying posts in the government and the concessions were to reduce class consciousness and weaken the communists.
To understand the magnitude of difference, imagine if the US House of Reps (total seats 435) had 40 honest-to-god Communists in power, with another 80 left-of-Bernie SocDems : thats what the French legislature was like in the 60s and 70s.
Instead the US has 3 extremely mild SocDems who may or may not be grifters.
I hope you see the magnitude of difference here, there is no real way of moving the admin left and whatever minor leftward shift you may see is what the ruling class themselves, by their own accord, decide is necessary to keep the threat of civil unrest from getting too high.
So whenever you see any liberals IRL or online talk about how we need to become like Norway or whatever, remind them No Communists in govt = No European style Social Democracy
Another example is the Young Lords getting garbage collection policies implemented in poor neighborhoods by outclassing the government in activism and work there. Civil rights came because of the split threat of the communists and the Vietnam War splitting need of use of force with black radicals at home.