Ice Cube is opening up about why Lamar Odom was cut from his BIG3 basketball league -- explaining, "We want players that are actually playing."

As we previously reported, 39-year-old Odom was axed by the league on Wednesday -- essentially ending his dream of returning to pro ball. 

Odom was a member of the "Enemies" -- playing alongside Gilbert Arenas and Royce White. 

But, Odom only posted 2 points and 4 rebounds in 3 games and our sources told us the guy simply wasn't ready to play. 

Cube echoed those sentiments at LAX ... "You know, as a league we want players that are actually playing."

He added that players who aren't playing or who "can't play" or have "health issues" that prevent them from playing really don't have any business being on a BIG3 roster.