I mean, there’s a whole bunch of reasons, but I don’t think it’s simply stupidity.

Some people didn’t learn the critical thinking skills you have, some may well have “lost their job to an immigrant” (and not realise that it was actually their boss that fired them because they can exploit someone more vulnerable than them). Some are scared of change, some are suspicious of “outsiders” and haven’t actually met any, and when they do realise everyone is just people.

And some are just dirty fucking racists, and they are absolutely stupid.