Ricky Bell,
Michael Bivins and
Ronnie Devoe were the three guys left after all the other members of
New Edition had released solo albums.
Bobby had left in 1986 (as mentioned above by danlowite) and had put out a number of albums. Then Johnny Gill released his highly successful album Johnny Gill on Motown in 1990. The final straw must have been the release later in 1990 on MCA records
of Ralph Tresvant's self titled album, which spawned the single Sensitivity.
As they said on their remix album WBBD-Bootcity, "The three left alone on their own."
Faced with the realization that they didn't harbour enough talent individually to come out with successful solo joints, the formed BBD. Their philosophy was " Our music is mentally hip-hop, smoothed out on the R&B tip, with a pop feel appeal to it."
Their debut album Poison sold over 3.5 million copies.
On a personal note, it took me a long time to convince a shop keeper, any shop keeper to let me have/purchase a no-go wafer so that I could hang it off my jeans, just like on the remix album cover.