I know that Americans hate to admit it for some reason, but it's just a historical fact: the reason social democracies exist in Europe is because of the Soviet Union. Most countries with universal health systems adopted them between the 1920s and 1950s as a direct response to the rise of communism in Eastern Europe. Adopting a social democratic policy as an "alternative" to communism to avoid the collapse of western capitalist countries would offer similar things that the communists offered, but within a capitalist society.
The Soviet Union had universal health care that more than doubled the life expectancy of its population. General education, including the university, which eliminated widespread illiteracy, and universal housing made it one of the few countries in the world where homelessness, etc. was ever eliminated, relatively poor country.
Together with the superpower of the world and the second most powerful country in the world as well as the neighborhood to Western Europe, they had an enormous influence and communist parties became commonplace in Western Europe. The Scandinavian countries that Bernie always points to were the ones most influenced by the Communists. Finland literally had a failed communist revolution like Russia, although unlike Russia, the Reds lost in Finland and thus followed the path of social democracy and not socialism.
The reason for the existence of social democracy in Western Europe was that the capitalist governments compromised with the extreme left and instead formed left-wing liberal governments. Instead of risking the overthrow of the entire capitalist system, the rich oligarchs made huge concessions and gave the workers the same benefits that the Communists offered, making the Communists less influential and people less concerned about overthrowing their government and to make the West more stable.
If social democracies in Western Europe gained popularity in response to Eastern European socialism, the collapse of socialism in Eastern Europe should also lead to the withdrawal of these social democracies and a return to neoliberalism.
And that's exactly what we've been experiencing all over Europe since the 1990s. The trend towards mass privatization and the dismantling of these social democracies has been going on throughout Western Europe for several decades. The Finnish government has collapsed twice recently because mass privatization has been massively suppressed. The UK was also in the trend of mass privatization. Royal Mail has recently been fully privatized. We now know that plans to privatize the NHS are in the pipeline.
This is the big elephant in the room that Social Democrats like Bernie Sanders and his followers ignore. They ignore (1) the reason why the social democracies came into existence and are therefore unlikely to be created successfully, and (2) ignore the fact that the social democracies to which they refer as replicating are currently falling apart.
Capitalism will not fix itself by going to rich oligarchs and asking them to be nicer, please. Social democracies were created by pressure from the left, the communists who tell the oligarchs that they will roll their heads. Social democracy was a concession, a middle ground between socialism and neoliberal capitalism.
People like Bernie want to go to the negotiating table and demand the middle ground first. That said, Bernie is likely to reach midfield of midfield if elected. It will neither get the strong reforms it is pushing for, nor will it likely stop the right trend that the world has been in since the 1990s.