"Why doesn't movement improve – even when you strengthen the muscles involved in that movement?
One theory is that the body adapts to move in the path of least resistance (not necessarily the best or safest path – just the easiest) and when something might change this preferred movement pattern (like changes in joint forces from stronger muscles) the body simply adapts to maintain it's old pattern. 5 This is speculative, of course.
More importantly, one must not forget the specificity principle. If the goal is to improve the strength of a specific muscle, then use targeted exercise. However, if one wishes to improve a particular movement or skill, they should practice that movement or skill specifically."
This isn't a great read, but the point is solid gold. You can't make a great athlete better by working specific muscles - the athlete needs to move better through natural movement patterns, and then needs to have strength built into the natural movement patterns.
That's why S&C programs use squats instead of hamstring curls and pullups instead of curls.