From their perspective, the Left have ignored and devalued them for years.

This is a very important point: the current technocratic left (and I'm really reluctant to call them "the left" because, frankly, they're right-centrists who don't care what you ingest or who you fuck) has been absolutely terrible about talking to people's fears and anxieties. At best they push concerns away with neoliberal knob-twiddling; at worst they demonize them, but in general they/we/the left have been extremely unwilling to be empathetic to working-class anxieties, either because no one wants to touch the status quo because it works well, or because playing to feelings is seen as crass and manipulative.

The reactionary right, on the other hand, as no such scruples: they've had this playbook ready since 1933 and are more than willing to talk about people's fears and anxieties.

It says a lot that the most successful and engaging left-wing politicians (Sanders, Corbyn; even Obama, to a degree early in his term) have spoken to these feelings. It's also telling that those politicians were ruthlessly attacked by their own party.