Why is the 'Populist' movement growing?

No one wants to see the misery and pain endured by migrants that has been outlined in this article,  Yet if allowed to enter the United States is there then not an ensuing misery and pain endured by American citizens (job losses, undercutting of wages etc?)
Of course none of that is of the proportion of a mother being
forcefully separated from her child as Ms Goldberg searingly
illustrates. But if one cares so much, one is drawn to ponder  how many immigrants are living with this journalist, has she housed any etc?  On a broader front, if Italy refuses to accept another ship packed with immigrants are they inhumane, ditto Malta;  ditto a growing consensus across Europe. Why is this 'populist' movement on the march, why are we increasingly hearing its voice. why are whole populations in growing  sympathy with this development?  Is it empirical economics, or is it visceral, or is it a combination of both?
Lumping them all as 'deplorables' is not an answer.