Climate change fallout, politics, taxes, etc are all contributors, but I think it primarily comes down to supply and demand. The places that are still "hot" tend to be places that didn't rush to build a lot of housing in recent years for whatever reason. Cities in the NE are pretty much built out at this point. They can't sprawl much, and building "up" to increase density gets costly to the point that it's no longer easy money. So, supply remains low, and prices are more stable.
Places like Austin, the Sunbelt, FL, etc all built as much as they could because they were seeing crazy demand, and it was relatively cheap to build out/sprawl. But it seems they either overproduced, or the forecasts were wrong and now supply has increased and prices have decreased. I don't know that the bubble popped, but it does seem to be deflating.