Hi Alex,
I created a test project and was able to reproduce the same behavior that you were running into. I created a user role called TestAdmin, and gave it the same module roles as the administrator user role. The only difference was the managed user roles was set to only manage one user role (in this case the user role was called user).
When I went to the account screen and tried to set an account with the user role user to inactive, I wasn't able to view the active boolean widget.
After playing around with it, I found that if I set TestAdmin to manage User and TestAdmin, I was able to see the active boolean on the account screen.
So for your TaxiAdmin user role, set it to be able to manage TaxiAdmin, Guest, TaxiAnon, and TaxiDriver. Hopefully that fixes your issue.