Politicians don’t see non-voters as a safe bet. It’s a lot more likely they won’t show up regardless of what the politicians does. From their perspective it is safer to try and sway people who do vote and might be able to be persuaded. Democrats aren’t going to vote for Trump regardless. The easiest path to victory is to convince the 1/3 or so Republicans who don’t like Trump that another 4 years of Biden won’t be so bad. That’s enough to win.
Edit: not saying I agree with this, just that is the argument.