In my experience, 9 times out of 10, people just need a person to workout with because they don’t like doing it alone.
It’s not necessarily that people lack the knowledge or skill or ability, they just for some reason or another cannot workout alone. That’s where trainers can come in handy! A trainer can help you maximize your workout. A trainer will sometimes workout with you. A trainer is there with you when you workout so someone is seeing how responsible you are and how well you are doing!..
I think most people need reassurance that what they’re doing is right and ok for them. A lot of people see working out as unnatural because it can involve weird movements. A great trainer can make working out seem natural by applying real life scenarios to the workout. Of course, we all know that! =)