From election strategy point of view, you are in a much stronger position if you poll much higher, for various reasons:
- uncaring and undecided voters, if they had to vote, are likely to vote for the winners, because being on the winning side makes them feel better (which may have decided this election)
- if you lose the election, people are more likely to believe that the other side cheated if you were projected a clear winner by the polls, so you can bring people on the streets or run fraudulent lawsuits to deter the opponents and still get a lot of support
So, strategically, it pays to poll higher regardless of how things really are. Given how a lot of media organizations are against Trump, it's not unlikely that these polling organizations were too... and they helped the opponents.
- uncaring and undecided voters, if they had to vote, are likely to vote for the winners, because being on the winning side makes them feel better (which may have decided this election)
- if you lose the election, people are more likely to believe that the other side cheated if you were projected a clear winner by the polls, so you can bring people on the streets or run fraudulent lawsuits to deter the opponents and still get a lot of support
So, strategically, it pays to poll higher regardless of how things really are. Given how a lot of media organizations are against Trump, it's not unlikely that these polling organizations were too... and they helped the opponents.