The biggest reason why amateurs get to a performance plateau and then quit improving is life circumstances do not allow them to practice more. Job, family, other hobbies, friends etc. limit their time so you really can't get better.
For the players who have all the time in the world to play and still don't improve are those who lack tactile (body) awareness. They never feel their back, legs shoulders, head or what their eyes are doing during a shot. They never develop the feel of a well executed shot. They do the same terrible technical stuff shot after shot after shot. Filming yourself helps with this but nothing replaces just taking the time to feel your core and head and shoulders while you are shooting. When I am at my best I can stop my gigantic head from moving when I am shooting a power shot. A pre shot routine should include getting the body settled and locked down. You can't do this if you never feel your own body.
For the players who have all the time in the world to play and still don't improve are those who lack tactile (body) awareness. They never feel their back, legs shoulders, head or what their eyes are doing during a shot. They never develop the feel of a well executed shot. They do the same terrible technical stuff shot after shot after shot. Filming yourself helps with this but nothing replaces just taking the time to feel your core and head and shoulders while you are shooting. When I am at my best I can stop my gigantic head from moving when I am shooting a power shot. A pre shot routine should include getting the body settled and locked down. You can't do this if you never feel your own body.