Some connected with the Dolphins team think they intend to stock the team with high draft picks and free agents and see what Rosen can do. They aren't playing him right now to protect his confidence as putting him out there behind the worst line in the NFL and with no rushing game would cause him to develop horrible mechanics and he would never learn to work his progressions. He'd basically become David Carr 2.0, a quarterback with all the intangibles and ability you want but one who got so pummeled in his early seasons he never reached his potential.
If Rosen ends up being bad next season with the team restocked then they package the multiple first rounders they have in 2021 to move up and get Lawrence or Fields.