You do recognize that Biden could have historic performances in many of these counties (kinda like how Hillary Clinton did in 2016) and still lose the electoral college?
Joe Biden could gain tens or hundreds of thousands of new votes in states like TX, GA, FL and NC (irrespective of the margin) and still come up short in flipping those states. Based on the aggregate predictions on this site that's what many posters believe will happen, in fact.
The great thing about the electoral college (for Trump) is that it doesn't matter if he wins TX by 800k, 80k or only 8k votes. He still gets to walk away with 38 electoral votes. Similarly, it changes the electoral calculus absolutely zilch if Biden bests Trump in CA by 6 million votes (as opposed to Clinton's 4.7 million).
I think people here are aware of how the electoral college works. The implication is moreso that if Trump is losing TX by 8k votes, he's probably also losing AZ+NC+GA+FL. Nobody's arguing that Biden winning CA by 39 points means Biden will win TX by 5, but that trends that can be seen in a poll in CA are not completely isolated from the rest of the country and are good signs for Biden among demographics he's polling very well with in CA.
