The media relied in the past on sophisticated sampling techniques that started breaking down when cell phones started to replace landlines, and collapsed totally due to the high percentage of people using mail-in ballots (which in the past were largely limited to people who couldn’t get to the polling place on the election day).
The US is hardly along among federations of choosing a head of state in a system designed so one region can’t force its candidate on the country over the objection of other reasons. The Democrats are very popular in the urban areas along the coasts, and the Republicans are the leading party in the rest of the country.