An interesting observation, GOET. Perhaps the following may add some insight.
But when you compare the polls to votes — Republican primary and caucus results — the bulk of evidence suggests that there aren’t many shy Trump supporters.
Indeed, there’s little reason to think that we’re in for a surprise in the general election because of Trump outperforming his polling on Election Day. As Cohn pointed out, the difference in Hillary Clinton’s margin over Trump between live-interview and online polls is fairly small right now at 2.5 percentage points, and that may have more to do with how the horse-race question is asked than the survey mode. This doesn’t mean that Trump won’t greatly outperform his polls or that people won’t be afraid to voice their support for him. But when you look at the evidence from the primary season and the general election survey results so far, I would bet on the polls getting Trump right again.