This hasn’t just appeared out of the blue in the last 5 years or so
WB have wanted to make a sequel of some kind since the release of the original in 1996. In 1997 they even began developing SJ2 with a new villain called Bersek-O. However Jordan did not sign on to be in the film so WB ultimately cancelled the project
other types of films were considered as well
Jackie Chan was considered for Spy Jam
Jeff Gordon for Race Jam
But those films were scrapped for Back In Action
The closest we got was Skate Jam with Tony Hawk which began development after Back In Action but was probably cancelled due to BIA poor performance
But nothing came of those ideas until Lebron James came on board in 2014