Formation of the American South Conference sounds reminiscent of the formation of the Great Midwest Conference (1991). Five of six original GMC schools left conferences which already had automatic bids to align in a more "marketable" format. UAB left the Sun Belt; Marquette and Saint Louis left the MCC (Horizon); Cincinnati and Memphis State left the Metro; DePaul was an Independent. Cincinnati, Memphis, and Saint Louis had all been in both the Missouri Valley and Metro Conferences together at some point prior to the formation, similar to how Louisiana-Lafayette was reunited with Arkansas State, Lamar, and Louisiana Tech from the Southland. New Orleans received a national ranking and NCAA berth in 1987 (Benny Dees, later at Wyoming) as an independent, and had achieved moderate success (well a title or to at least) in the Sun Belt Conference prior to leaving in the early 1980s (I have no idea why UNO left its initial membership, but I am very curious). Perhaps Texas-Pan American can be analogous to UAB, but admittedly that is probably a gross oversimplification.
Saint Louis finished as runner-up in the NIT (1989-1990) as a member of the MCC, was scheduled to be moving into a much larger arena (Kiel Center), and arguably had a greater basketball tradition (at least at the time) than the majority of other then-MCC matters (this is obviously still subject to debate).
DePaul and Marquette were long-time Midwestern independents, along with Notre Dame, and later GMC member Dayton.
UAB felt that its stature necessitated that it had "outgrown" a Sun Belt Conference that had become somewhat stagnant by the latter half of the 1980s.
Not exactly sure why Cincinnati and Memphis State left the Metro, but it is generally conceded that throughout its history the conference more or less revolved around Louisville its only continuous member (Tulane does not count as a continuous member due to the four-year shelving of its basketball program).
Good points about Lamar. I forgot about the successes of the basketball program in the late 1970s/early 1980s (e.g. Billy Tubbs), and yes football would be terminated two years into American South membership. Louisiana Tech (e.g. Andy Russo, Karl Malone) had also had moderate success and was even able to obtain an at-large bid (albeit as a #16) in either 1989 or 1990. Not clear on the basketball histories of Arkansas State, Louisiana-Lafayette, or Texas-Pan American. To clarify a point from yesterday, Louisiana-Lafayette left the Southland after being the only conference school not to be dropped from the I-A ranks in 1982. Louisiana Tech would later rejoin the I-A ranks (1989?) as would Arkansas State (1992, whatever happened to Ray Perkins?). Obviously whatever shortcomings the American South had in the way of recognition of its achievements would later be rendered moot when the conference was merged into the Sun Belt in 1991.
Ironically, enough the only remaining American South members (out of a total of seven) are Arkansas State, Louisiana-Lafayette, and New Orleans. UCF left after the first year, Lamar and Texas-Pan American after five and six years, and Louisiana Tech for the WAC for reasons relating to football.