This can be explained.
Since players can have maximum of 200 CA and PA, it makes impossible for one player to have all 20's. Why?
1) Not all attributes consume CA the same. Mental uses more CA than Technical, but then Physical use more than Mental. Also, to grow from 19 to 20 consumes more CA than from 1 to 2. Also, one thing that influence the CA massively is weaker foot. Since 1 + uses aprox 3 CA, having 20, 20 ( left foot 20 and right foot 20), it will use aprox 60 CA just on his weaker foot. Best thing you can do is to make player almost perfect for specific role. Like having one foot set on 20, and other on 1, and make key attributes for that role set on 20 (every other attribute, lets take for example you are trying to boost someones poacher ability. You don't really need tackling and marking, as well positioning, long shots, corners.. you get the idea. You need to make those attributes as low as possible ( lowest possible is 1, zero makes that attribute random), CA and PA should be 200.
2) Some attributes cannot be affected by training, like Natural fitness, flair, work rate, team work, bravery, aggression and determination. GK's attributes that cannot be affected are Eccentricity, rushing out and one on one. Those attributes increase by natural progression - gaining experience through playing games. That said, they cannot be decreased unless they suffer injury or having no playing time ( most of them can, some can't), and because of that, FM will always use CA from attributes that can be decreased by training to balance that player.
