I think it was the 2 parties becoming more clearly delineated on social issues, Clinton in the 1990's to some extent had managed to keep the realignment from occurring via his policies on issues like crime.
Gore made it clear in 2000 that he supported Clinton’s crime policies, and I don’t recall Clinton being socially conservative on any issue besides crime. Clinton was as anti-gun as any Democrat today, if not more so.
Bush was clearly more socially conservative in terms of his appeal than Dole though, Bush didn't try to downplay his religion but embraced, it was pretty clear who was more socially conservative and which candidate was more pro Christian, I think that had a big impact on voters.