Materially, it makes little sense for blue-collar workers to vote for Modi, Orban, or Trump, a billionaire whose platform is to cut taxes for the rich. Hitler and Mussolini had their share of support from the poor too.
What are some of the theories of why this happens?
I know scapegoating foreigners for poverty is part of it. Wilhelm Reich wrote The Mass Psychology of Fascism but I haven't read it.
There's a few, but one is atomisation. Blue collar workers have a better deal but have been atomised from wider struggle either at the factory or industry level. So what they do have is entirely focused on self interest. Sympathy strikes being made illegal was a key component of shutting down mass organisation.
As for service workers, isolation and small workplace numbers along with long and irregular hours mean that they've always had trouble organising. Maids and Serving staff were one of the few groups to fail to get real workplace protections in the late 19th/early 20th century. This may be changing, but currently the ruling class sees no reason to change the usual tactics of keeping them atomised at the individual level.
If there's no solidarity between groups of workers, those workers will turn reactionary to protect their own station. And practical solidarity these days almost always means risking your jobs and breaking the law, for someone else's fight that probably wont succeed. That's a hard sell.