I agree that your two examples don't stand up to scrutiny.

There is historic precedent for blaming immigrants (as an example, or just others, if you like) for one's woes. So on one hand you have well-known "playbooks" that don't require some secret meeting of a cabal.

That aside though, even if actors don't collude, if they're each throwing a lot of things at the wall, they may well all arrive at the same things that seem to "have stuck". It's as though there are universal fears and even prejudices among populations of people.