The big reason for polarization is a voting system that directly causes it. Single winner elections, where the candidate with the plurality of votes wins, will

The big reason for polarization is a voting system that directly causes it. Single winner elections, where the candidate with the plurality of votes wins, will automatically cause polarization (see "Duverger's Law"). All the more so as candidates and their campaigns get more scientific about how to win. Because smart candidates will try to avoid having their vote split, plurality elections have two sweet spots, "middle right" and "middle left." Anywhere else is generally a no-man's land. Some things about TV and deregulation might contribute to it, but there are enough channels and enough other options for consuming news that I am not convinced that is a big part of the problem.