Also old and crotchety here. When I was young, back in the Dark Ages, in the rural-ish mid-west, lower heights were for equitation classes at local shows. After that you were showing hunters: 1st year green, 2nd year green, and working hunter (3’6", 3’9", and 4’ ? My memory is a little fuzzy on that). Show jumping was only a thing that happened at big shows and was way out of my league.
And I think it’s true that the vast majority of trainers in most parts of the country are not developing many riders who can develop their own horses or don’t need the prefect packer. I think many trainers today in many parts of the country aren’t capable of doing so because they never learned themselves and many who are capable are simply providing what the market dictates, which isn’t that kind of program.
I’m not criticizing anyone, I think it’s just a reality of the situation. And I’m not being cynical (although that is my default setting) - I don’t think trainers make a conscious decision to not develop riders/horsemen. Some of them simply lack the ability to do so and for some, their clientele too often don’t have the time/money/single-minded obsession to progress to that level.
I think there are still parts of the country where you will find trainers who can/will develop riders/horsemen who can jump larger fences and train their own horses. There just aren’t nearly as many as there once were and there are parts of the country where there aren’t any at all.