Not everything is about fit ... New England broke hard toward good ole boy Bill Clinton from Arkansas who, according to quotes from Carville and others on the campaign that I have seen, was VERY intent on showing he was the Democrat who could regain the South. He actually did a very good job of that (I remember seeing one time that Clinton was apparently furious he didn't flip Texas), all the while picking up a lot of Northeastern suburbs.
Additionally, it was former Massachusetts Governor Mitt Romney, a Mormon who was regarded as a very moderate governor during his stint and was attacked all throughout the GOP primaries as "not a real conservative" or whatever, who led the complete collapse of Democrats in many ancestral Southern areas. At the time, people pointed to how all of the racists had abandoned the Democrats already because Obama was Black, but we obviously saw that talking point 110% backtracked after 2016 so that they could save face. 
Carter won Los Angeles County, IMO, because Los Angeles was very Democratic already (urban voters were Democratic, regardless of "culture"), and it carried enough of the population to sway the county.
I agree with almost all of this, but re: the bolded part I’d add that Clinton didn’t do particularly well in the South in 1992/1996 for a victorious Democrat despite being aided by Ross Perot, who almost certainly cost Bush GA (and arguably KY) and Dole KY (and arguably TN). Even with Perot winning 22% of the vote in TX, Clinton became the first Democrat to win without that state.
Hot take: I think even Carter's showing in the South in 1980 (especially in rural areas and small towns) was more impressive than Clinton's in 1992/1996 when you factor in the environment and different fundamentals, it’s just obscured by the fact that the poor guy lost so many Southern states (and MA + NY) by hilariously narrow margins, which makes the map a little deceptive.
