IIRC there is some research in psychology that seems to prove this. It involves a questionnaire about political topics in which you take a representative sample of people on the left and right, then split that population into quarters. One half is told to answer the questions truthfully, as they believe. The other half is told to answer in the way they think someone with the opposite politics to themselves would answer.

The results are then compared. The findings are apparently always the same when this is done: conservatives pretending to be left wingers give answers much closer to the real left wingers than vice-versa. That is, the right understands the left but the left doesn't understand the right. It's been some years since I read about this but iirc the failure mode was that the left imagined people on the right as having far more extreme views than they really do, amongst other problems.

W.R.T. the construction companies - see my comment elsewhere in this thread about the quote-sourcing feedback loop. Not so many companies are willing to talk to journalists about illegal immigration, because they know journalists are left-biased and because it'd realistically have to be the CEO doing it, and he/she is busy. That in turn means journalists don't hear alternative perspectives, causing them to become more biased, and repeat.