Because basically no other metric besides polling suggests any sort of Trump landslide. Midterms and special elections. Donations and fundraising. Campaign offices and ground game. Demographics and demographic changes in key states.
Because none of these metrics matter. And demographic change is pointless when within that demographic you see a mass drop in turnout.
If demographic change in states was all that mattered, really you could write in the winning party from 2024 to 2052 basically with 100% confidence.
You can make the same argument polls don’t matter because they aren’t actually real like election results and donation numbers.
Also Demographic change does matter because in a state like GA, it gives Biden a bit of a cushion to perhaps like with black voters for instance. It doesn’t guarantee he’ll win the state but certainly helps him.