It is much easier to get into debt than to get out of it.

你的理解是对的，这里的不定式不是什么目的状语，而是作主语的，相当于：

To get into debt is much easier than to get out of it.

你的疑问是：我怎么感觉这里的不定时其实是做主语啊，那这样的话，为什么说成非谓语动词呢？——你认为“非谓语动词不能作主语”，是吗？错了，其实，不定式和动名词这样的非谓语动词是可以用作主语的。又如：

To act like that is childish. 这样做是幼稚的。

To accept their offer would be foolish. 接受他们的帮助是愚蠢的。

To say is one thing, but to do is another. 说是一回事，做是另一回事。

To affect a policy is to have an effect on it. 影响一项政策就是对该政策具有一种影响。

To marry a woman for her beauty is like buying a house for its paint. 由于面貌美丽而娶妻，犹如油漆漂亮而买屋。

To boot (up) a computer is to load an operating system into the computer’s main memory. 引导计算机就是指将操作系统加载计算机主存储器。