They would have kept UConn if they wanted to balance out Navy's football program.
BSU is living in the glow of its past glory. It hasn't been a player, on the national FB scene since the 2014 Fiesta. Since then, the AAC hasvgained 4 berths in a NY6.
In basketball, the current AAC members have more than three dozen appearances this past decade and more than two dozen appearances beyond the first game ( I did not include UConn's numvers). BSU has two NCAA tournament appearances, never advancing beyond the first round.
BSU doesn't bring anything special to the table.
The ACC holds the high ground. They are doing very well, without BSU. And they haven't forgotten that BSU once reneged on a contract to join the AAC.
If the conference is interested in BSU, should the latter consider moving on, they will demand all sports.