Even if the polls are as wrong as they were in 2016, Biden has enough of a cushion to survive a last-minute dropoff. It would take an unprecedented amount of error for Biden to lose, assuming the numbers are unchanged over the next few weeks (which is doubtful, Republicans will eventually consolidate). But since you can't really control poll error, it makes sense for Biden to play it safe. It really makes no difference whether Biden wins in a landslide or with exactly 270 electoral votes, and he is enough of an establishment crony that he probably doesn't care about downballot ramifications since he is completely devoid of any ambitious policy proposals. In that sense, it's a smarter play than the Thatcher campaign's overreach in Texas and Georgia.

nobody can figure out a voterfile to coherently poll Nevada

nobody can figure out a voterfile to coherently poll Nevada Doesn't help that Nevada is one of the most transient states there is. Still, a place that favors hospitality employees and people exiled from California by a high cost of living (hello!) is unlikely to suddenly lurch back to the right.