It simply wouldn't have been possible for the models to be more accurate with the data they had. As they say, bad data in, bad data out.
That's why this time around the pollsters made sure to be more thorough in their polling.
"This time is different."
I've heard that enough times to be highly skeptical. I'm also deeply skeptical of the notion that polling is even remotely correlated to actual results. Cultural and historical trends play a drastically higher role and are almost always left out.
But it has been strongly correlated to the results in basically all elections so far in all democracies on the planet. Taking 2016 as an example there has been a very strong correlation between polling and the results. The national polling averages were only 3 points off from the actual result. If that's not correlated I don't know what is.
As for fear of doxing: plenty of people openly supported and voted for George Wallace (a noted white Supremacist) back in the day, and even Roy Moore (accused pedophile) just 2 years ago. Proud Boys members openly pose for the cameras even as they espouse racist views, and QAnon members brag about being part of QAnon.
The purported shy Trump voter? Doesn't exist. https://fivethirtyeight.com/features/trump-supporters-arent-...
Not every Trump voter is a "Proud Boy" or noted white supremacist, maybe even some of your friends are who "just aren't interested in politics" because they know that if they were honest with you, you would flip out. Some understand that this attitude about yard signs is actually representative of an entire worldview, and opposing that might actually be the lesser of two evils.
Essentially I think that those narratives about one side "shutting down" the other side are not true for either party. In my opinion they are mainly the result of filter bubbles where you are constantly presented to all the outrageous things that the other side is doing (the above mentioned article is clearly an example) while actually people remain largely civil and are not tied to their political identity in such an extreme way.
It's also likely this works in both directions - if you support Biden, I bet you don't have a yard sign for it if you live in Mississippi.
By construction, the effect is strongest the more you're not in the majority, which also means your unspoken support is more likely to not matter on the actual outcomes of the election.
Newsflash, they aren't, so your hypothesis must be they're too shy to admit their Trump support to a machine?
Everybody is just fighting the last war where Trump suddenly won for a couple of reasons. So, the Dems are scared they are missing something, and the Reps are going "Haha, who cares about modelling".
Will, the forecasts be perfect? Nope. But is the margin rather large, but not unsurmountable? Yes it is. Are the mistakes from last time repaired? Yes, they take care of uneducated whites. Is there evidence Trump has found a new source of voter support? I haven't seen it.
If anything, Trump supporters have been extremely vocal about who they were supporting, to the extent that they frequently violate social norms and try to takeover events and gatherings to make their political affiliations known, like this week with Among Us.