The team ultimately made this decision for him. The thinking was that it wasn't worth moving Bo off of the position for a player that was likely to be a one year rental. If I recall correctly they said that he could only be moved off of short stop once, as sending him back to the position after moving would be incredibly hard to do. It would be far more prudent until they are completely convinced he is unable to be the long term answer at short stop. The results of the last two seasons aren't exactly encouraging, but I still think Bo has the necessary tools to man short stop effectively. What remains up in the air is whether he can ever develop the kind of consistency that is required. He has had extended stretches were he plays a really good short stop, but then he goes through even longer periods of time where he struggles to make the routine plays.
Bo was reportedly willing to move off short stop years ago for the likes of Didi Gregorius to allow the team to upgrade around him, I just don't think this idea that Bo has been refusing to move from the position has any kind of proof behind and is rife with assumptions.