Given the very negative environment for many Trump voters, they’re going to be very sensitive who they trust around that topic.
When a pollster calls, the polling company have your number and can in all likelihood get your name. Can a Trump voter trust that he isn’t going to get doxxed? Given the degree to which the progressives have been promulgating and supporting “cancel” culture, that’s not a farfetched concern when one has a wife and family to support.
So some either tell the pollster they’re voting for Biden or more often if they’re like me, they don’t take the call because they think it’s just another junk call.