To learn English well needs much practice.为什么不是说learning English well needs much practice.

差不多一个意思.
to do 和 doing 作主语差别在：
to do强调没有做的事,即将做的事.To learn English well needs much practice——对于这句话,我们可以翻译成,要把英语学好,需要练习.
doing 强调状态,陈述事实的感觉.learning English well needs much practice.---这句话就应该翻译成,学习英语是需要练习的.
恩,应该就是这样.