People look at the big picture in polls(X candidate is leading in polls) and then say they're wrong when Y candidate wins, but it's way more nuanced than that.
The 2016 polls were not that far off. Hillary won the popular vote, as the polls predicted. The key states she lost, she lost by small margins within, or not too far from, the margin of error.
If you look at FiveThirtyEight's final prediction for 2016, Trump had a 28.6% chance of winning. That's between a 1 in 3 and 1 in 4 chance! But the media narrative was that Trump had 0 chance, and what happened happened.