I have dark brown (no grey!) rather fine hair and I wear it long.
The problem for me with having it short is that it requires a skilled hairdresser to cut it well, as it is so fine and flyaway. As someone else has said, when it was short I would wake in the morning with one side sticking up in the air and it was the devil's own job to get it to go where I wanted it to go.
I am a lazy soul and faffing about with potions to try and make it stay where I wanted it and all the blow-drying etc was definitely not how I wishes to start each day.
I have a fringe; and never wear my long hair loose - I plait it (one or two), tie it in a 50's pony tail, create a scrappy twist up in my head etc. It is so easy and no "products" needed. I can also do my hair without the use of a mirror - I often do this if it starts to fall out. Work of a second and no faff!
I am not good at posh - and smart hairdos are simply not me.
As I have said on this site before my hair is nipple length, and this initiated a discussion as to length of nipples!
To address the OP's point - I do agree that people seem to get to a certain age and cut their hair short as some sort of rite of passage - look folks, I am middle-aged now!!
. I too have often wondered why this is.