That's because they are wrong, immoral, and stupid. They're grovelling in the crumbs left over by the rich, and then getting pissed that there are other people groveling for the same crumbs.
Blaming immigrants is easy because you get an immediate base amongst racists (the immoral). They'll perk up at the sound of your dog whistles, and immediately start barking shit like "finally someone had the bravery to say what we're all thinking". That amplification of your message then reaches the reactionaries, who accurately look around at the world that is hell bent on destroying them, but are a little too dense to understand the web of systems that make up that world, and thus are eager for a simple explanation (the stupid). And once your message gets embedded in the zeitgeist from that lot, normal, relatively detached from politics people start hearing all this talk about immigration being a problem, and believe it (the wrong).
The same way you can't be frugal to make up for making poverty wages, you can't shrink the pool of disadvantaged workers to make them advantaged.
Sorry, you speak about this as though you are an American (not sure if you are) but you can't hope to understand the realities of living in a country that just injected 1/10th of its population in a decade.
The demographic of the largest cities in Sweden has changed from 17% foreign born in 1986 to over 55% today- in a single generation. (Malmö, were I live as a migrant myself).
At the same time, the healthcare service is struggling, the police can't cope with the crime situation and there are gangs shooting people and grenades blowing up apartments everywhere.
AND: At the same time, the Geni coefficient remains remarkably low, and income inequality much lower than the US, so this "blame the rich" makes sense in the UK and US, but it's not the problem that Sweden has.
Sweden has mismanaged a lot of its public services (training, then underpaying doctors - leading to them going private, then there being a shortage of doctors which leads to the government paying huge contractor rates for those doctors - which is hugely expensive, so nurses try to avoid you seeing a doctor - which leads to less preventative healthcare, and more serious issues, which is more strain on the healthcare service).
It's not uniquely immigrants fault, they have a role to play in the welfare system and being hugely overrepresented in crime, but it's really not rich peoples fault.
Not in Sweden.