From what he was saying, stress, depression and dietary deficiencies are the other factors. Vitamin D, Zinc, Magnesium and "good fats" are all required to maximise natural production. The other two aren't as clear cut, as low T causes depression...and depression causes low T. So once you're "in the hole" so to speak then it gets harder to get out and the effects snowball in a holistic fashion. High bodyfat causes low T, but having low T makes it harder to lose bodyfat etc.
He said there is a chance I could get my levels up for a while, lose some bodyfat and focus on sleep, and later down the line reduce or eliminate the treatment to try and kickstart production again.
He has a guy in his early 40's who came in at 33 with 130ng/dl, took TRT for 4 years and then reduced down. He has a natural level of average 520ng/dl now and just takes a mild AI to stop estrogen conversion. So it isn't necessarily a lifetime thing either.