Canadian observer. Two things, and I think they're related effects.
Harris is a minority and a woman. The Democrats were convinced they were the party that minorities would automatically vote for. But what they failed to realize was that those same minorities are misogynistic as hell. Like, have you ever been to a Baptist wedding? If you ask them what the role of a woman is...
The US is also the only first world country where the birthrate is above replacement. But if you look at who are having children, you'll find that it skews conservative. And they're passing those values along.
The thing is that the party conceding here actually trusts the election process. And Trump most definitely won the electoral college.
Even if he ends up losing the popular vote eventually, it doesn't really matter. The system is rigged and has always been rigged in favour of land over people.