Problem is that polling would have to have all the exact same behaviors as an actual election

• The ballot boxes don’t come to the people, the people opt to go to the ballot boxes. So cold calling/mailing people means you’ve changed the engagement to include people that wouldn’t actually go out to vote. Some try to measure likelihood to vote, but if the reason is ‘laziness’, a lot of people are unlikely to admit they won’t vote.
• Some population sees the polls as a strategic tool, and may modify their participation to advance what they think their outcome needs. Declare support for the opposing candidate to put the fear of losing into like-minded voters, for example.
• People know the polls don’t actually decide anything, so even if they will vote, they may dismiss polls as a waste of their time. Or even being distrustful of the agenda behind the poll and decline to participate thinking that works best to undermine potentially malicious polling
• People have more confidence in the ballot being secret than polling. If someone thinks their answer will be seen/overheard by a spouse, that may change their tune. If someone thinks something vile would actually be in their benefit, they may be reluctant to admit that, but happy to act on it at the ballot box.

Now polls are better than “gut feelings” or “this person posted to social media their gut feelings”, but the ultimate answer is we have no way of accurate prediction, so don’t be encouraged or discouraged too much and just go vote.