Because its a well known pattern that anybody who spends 5min looking at the data knows. Most immigrants live in cities that mostly vote left. The places that vote right are rural places that barley have immigrants.

Hence you have places like Fox news run coverage about cities all the time, telling you how they are lawless places full of crime. Scaring rural people about what all these immigrants will do once they final start to move to bum-fuck nowhere.

You seem the same pattern in most democracies.

There is no correlation between contact with immigrants and anti-immigrant voting.