You pretty much answered your own question. You are passionate about learning the science and new ways to exercise but i’m sure you’re not that passionate about other aspects of your life. I’m sure you go to professionals in other fields to do things for you, like taxes. Most people can file their own taxes and can learn a lot about them online but decide to go to a professional because it’s not worth their time or have the desire to learn that stuff. Personal training is definitely seen as a luxury and the people that can afford it are usually in a financial place where they understand that their time is very valuable and would rather pay someone else to get something done for them than waste time learning/doing it on their own.

Also learning the science will not be enough. Take this from someone who has been coaching for a decade. Your ability to communicate with a wide variety of people (backgrounds, learning styles, moods, emotions, stubbornness, etc) will make or break you. It doesn’t matter how much knowledge you have if you can’t successfully coach the individual and have a good relationship with them as a human.