Change is hard!!! It is hard to mentally accept that there is another way of doing things with your horse. Not to mention muscle memory just makes things happen the way you have trained yourself to do it.
When you have been doing things a certain way with your horse for so long, it is easy to not think about doing it another way. Especially if what you are doing is working. If you are used to holding the horse in a position with solid rein contact and constantly pushing with your leg, and you get the movement that you want, why would you change? Perhaps there is an easier way of doing things for both you and your horse mentally and physically. The goal in the art of riding is to do less and less as a rider and yet have the horse be willing to perform the movements happily on his own.
Many people get stuck in their thinking. For instance, if I don’t use my leg like this, he won’t move sideways or go forward. If I don’t hold him with my hands, he will not stay round. With this way of thinking, your horse will get heavier and heavier to the aids. Thus, making it harder and harder for both of you. It is a lot of work always to be kicking the horse to go forward. Not to mention, your horse will eventually become dull or resistant to all of that pressure.
If you make the conscious decision not to pull and hold or to not constantly use the leg, then you will have to find another way. In searching for this new way, you and your horse have another chance to find lightness and partnership with one another.