At least some credit goes to a guy named Antonio "L.A." Reid, a good but not great R&B drummer from Cincinnati who moved to Hollywood, realized his true talent was producing records, and in 1988 stopped playing in his somewhat average band altogether and switched to producing R&B full-time. This is all from his memoir, LA Reid: Sing to Me, which I guess counts as a primary source, but should obviously be taken with a grain of salt. Apologies if what follows sounds like a hacky music magazine article, but summarizing a self-aggrandizing account of someone's rise to power makes for bad prose.

In 1989, personal drama and a series of earthquakes in Los Angeles motivated Reid and his producing partner Kenneth "Babyface" Edmonds to consider moving to a different city and starting their own label. They chose Atlanta as a place that they felt was culturally exciting, a historical hotspot for black business, but not yet on the music industry's map. Reid recalls that in 1989, Atlanta wasn't well established even for basics like recording studios or equipment rentals. In their own words, they could be the biggest tree in the forest. They called their label LaFace Records and negotiated a loan/distribution arrangement with Clive Davis at Arista Records, a much larger operation in New York that had a lot of stars, but nobody with pop culture impact.

From there, dominoes started to fall. Reid found a group called Damian Dame that sent a single "Exclusivity" to the top of the charts in 1991. Arista was impressed and gave Reid the opportunity to work with Whitney Houston, one of their stars who they felt needed to "strengthen her grounding in contemporary black music", which went well. Meanwhile, the economy was strong and hip-hop and rap were beginning to break through.

Reid and his wife, Perri "Pebbles" Reid (herself a successful R&B singer), both had an eye for talent. Perri's hairdresser's assistant told her she was part of a trio called 2nd Nature. Perri invited them to audition, and husband and wife both recognized potential in two of the girls. They connected those two to a backup dancer from a Damian Dame music video who could sing, the three hit it off, and that was the start of TLC.

The same month, Arista recommended that Reid consider signing a group of five singing sisters that Arista was dropping. Reid invited them to Atlanta, discovered that only one had talent, but that one had a lot it, and convinced her to sign a solo deal with LaFace: that was Toni Braxton. Reid decided to market Braxton by attaching her to a movie soundtrack, and through contacts discovered Eddie Murphy's movie Boomerang, whose directors were willing to give Reid the role of creating the soundtrack. In addition to providing a platform for Braxton on a soundtrack that ended up selling 3 million copies, Reid also gave a track to Boyz II Men, who at that time were teenagers from Philadelphia who had just put out their first hit record. After they recorded their track for Boomerang, Reid flew them back to Atlanta and produced a second track for them, "End of the Road", which became a monster R&B hit in its own right.

In 1993, Usher’s mother recognized his singing talent and moved to Atlanta from Chattanooga in hopes of getting her son (then 14 years old) noticed. A LaFace employee at a local talent show happened to see Usher perform and brought Usher back to Reid for a formal audition, who immediately signed Usher, and used the same strategy he’d used with Braxton: getting him a single on a hot movie, in that case, Poetic Justice, by Tupac Shakur and Janet Jackson, with an accompanying music video, at which point Usher took off.

Also in 1993, Reid’s wife introduced him to a local producer named Sleepy Brown, who was part of a production team called Organized Noize, which brought two acts to audition at LaFace: one of those acts was Outkast, both members about age 17. They were initially unpolished, but Reid saw their potential and signed them quickly. That year, LaFace did a Christmas marketing campaign where they asked all of their artists for Christmas-related records, to which Outkast contributed a track that would eventually become “Player’s Ball”. The record went to number one in January 1994, and the debut album went platinum.

A third critical event occurred in 1993, which was that both Reid’s marriage and his producing partnership with Edmonds was ending, leaving Reid vulnerable and in need of producing talent to replace the people he was losing. This served as an impetus to move away from the smoother R&B that Edmonds had specialized in, and was further accelerated when Reid interviewed Sean “Puffy” Combs, a recently fired A&R man from Uptown Record, realized that Combs was more valuable running his own “street-oriented” label than assisting Reid with production at LaFace, and bankrolled Bad Boy Records.

In 1994, then, you've got Usher, TLC, and Outkast all wrecking shop in Atlanta, plus the takeoff of Bad Boy Records, and Reid continuing to act as a local conduit to the big leagues. This doesn't explain everything about Atlanta by a long shot, but it might give you some insight into what helped make the scene there coalesce and go national - and what put Outkast in a position to let the world know the South had something to say.