Why? Failures of neoliberalism. The increase in wealth inequality, the refusal to adress issues structurally, and the appeasement of fascism to name a few.

The fascist party is polling at 30% the party they split off in the 70s is polling at 20% it's not good.

https://www.sanders.senate.gov/press-releases/news-sanders-urges-president-biden-to-withdraw-support-for-10-1-billion-in-military-aid-to-israel-and-support-un-efforts-for-a-humanitarian-ceasefire/

Where does the idea come from Bernie would be seen as a moderate outside of the US? He openly ran as a communist when he was a mayor. His policies are far to the left to any social-democratic party in Europe.