Predetermined Protocols, Workouts, Assessments, Warm-ups, Reps, Sets, Volume, Intensity, Etc. You name it. None of them ever consider YOU!
Do you want to do the same workout as your trainer's last client? If so what's "personal" about yours?
Creating difficultly and creating progress are not necessarily the same. In fact they are more often completely opposite. Although progress does require challenge, there are tons of variables to consider. Almost none are taught in any of the industry's certifying bodies.
If your trainer is unaware of these variables how could they possibly manipulate them to customize your experience?