1) not all camera bodies include those fine tuning options in the camera firmware;

2) lenses that include additional buttons beyond that which the camera maker programmed the body to understand can't be tweaked by a body that was never programmed to know the button exists;

3) in the specific case of some Tamron zooms, the Tamron focus fine tuning is at up to five different distance figures, while most camera body focus fine tuning is a single global setting for that one lens;

4) for camera bodies that do include focus tuning in their firmware, they also usually have a limited number of slots for a limited number of lenses. For professionals they very well may own more lenses than the camera has slots, so being able to "tune the lens" via "the lens itself" means each can be fine tuned, even if the camera body cannot store that many different adjustments;

5) an adjustment the camera maker never thought to include (i.e., one example quoted in the repo where the focus ring direction can be reversed) can not be tweaked by the camera body. This is useful to photographers who mix lenses from different makers on the same body as Canon builds their focus rings to rotate one way when focusing towards infinity while Nikon builds their focus rings to rotate in the opposite direction towards infinity.