For these versions and many previous, tall grass is much less common in savanna, plains, extreme hills biomes than in the legacy versions of Bedrock edition and on Java. This makes many of these biomes sparser in comparison. This is a bug and not intended as stated by the community manager's post Reddit thread
I am aware that this has been reported previously but it was closed and resolved as "Working as Intended" and wish for it to be reopened and properly fixed.