As I write the latest count shows that Biden has crept into the lead in Georgia. If that holds up he would be the first Democrat to win the state since Bill Clinton in 1992. But it isn't really surprising, since elections over the past decade have seen Democratic candidates for governor and senator getting ever closer to winning. Right now it looks like both Georgia senate races will go to run-offs, and though Republicans would have the edge in both races they are very close, which shows the state becoming truly competitive again.
As to why, the experts mostly point to demographics. Georgia has about 10 million people, 6 million of whom live in metropolitan Atlanta. The population has more than doubled since 1970, with most of that growth in the Atlanta metro.
The racial breakdown is about 52% non-Hispanic white, 32% black, 6% Hispanic, 4% Asian; this totals to only 94%, which leaves 600,000 people of other, mostly mixed, ethnicity.
Besides immigrants from outside the US, Atlanta has had more than a million white and black Americans move there from other states, mostly in the northeast or midwest. It is the black migration back toward the south that attracts my notice, reversing 120 years of movement in the other direction. Those black people move to Atlanta for the same reason white people do, because they think they can make money, but also because it has a large black community that has produced many state and national leaders. It's a place where many black people are thriving, and where racial tensions are fairly muted, certainly no worse than in most northern cities.
For all intents and purposes, Atlanta is a national or world city like most big places in the US, having more in common with Houston, Indianapolis, or Denver than it does with rural Georgia. Because it so dominates the state, that moves the whole state away from old Dixie and toward national norms.