I'm American and it's never made much sense to me, either.

Afaik it's fundementally 5 forces.

• Severe distrust of the established institutions, including the democratic process.
• Long-drawn, multi-generational unrest ever since late globalization and the decline of unions.
• Anti-labor propaganda and institutional complacency.
• Increased alienation and in-fighting among the population. Got much worse ever since the MAGA repubs cropped up. We're fighting against 40-50% of the population for basic shit. (Have you seen our paralyzed congress?)

Finally, this unwillingness to be the first to bite the bullet. Inevitably, the first people to start off these grassroots movements are going to get the shortest end of the stick. They are people sacrificing their free time and economic security for a movement that begs others to do the same.

It's a massive risk.