The main 2 categories of people that need a personal trainer are:
- beginners that don't know what they are doing and will get no results and/or injure themselves
- elite athletes that need expert supervision to prevent them from training too hard and injuring themselves
The vast majority of personal trainers that offer their services to beginners are deliberately making everything as complex and as hard to understand as possible. They surround the simple act of training in a fog of mysticism and pseudo science.
100 different exercises with 100 different variations, every day looks different, custom rest time between exercises (sometimes measure in seconds), drop-sets, super-sets, up-sets, down-sets, everything-sets.
They make things as confusing as possible in order to keep you from learning how to do it yourself, because if that happens, you no longer need them and they are out of business.
The main role of a personal trainer should be to supervise your training so that you don't get injured, and log all your data (performance, training volume, body weight, fat %, bloodwork etc.) and make sure that you are making actual progress towards your goals.
Those people are very rare, and as a result they charge a premium $$$ for their services.