Bryant was never projected to be a good defensive 3B. If you thought he was the next Nolan Arenado (someone who never flashed elite glove potential but then was an elite glove), I assume the Cubs would move Bryant way less than they do. As it stands, the Cubs basically don't move a ton of starters around
C - Montero, Ross, Schwarber once a week
1B- Rizzo
2B - Zobrist, Baez, LaStella
3B - Bryant, Baez, LaStella
SS - Russell, Baez
LF - Schwarber, Soler, Bryant, Szczur
CF - Fowler, Heyward, Szczur, Baez (though never MLB)
RF - Heyward, Soler, Bryant
There are really only two guys who ROUTINELY move around - Bryant and Baez. Almost everyone else who is in the lineup is in the same place if they're in the lineup.
Baez moves around because he's a fairly elite glove who gives guys days off; Bryant moves around because he's not an elite glove but a great athlete (his best defensive abilities are tied to his speed/range/size combo) so it makes sense to use him in a utility way.