I don't know that OO's main goal is to be readable, but rather to manage complexity (which should help readability, but I don't think that's the focus). There's an inherent level of complexity in OO that isn't necessary when you're solving basic, learner type problems, but it can help keep complexity down when you're solving problems that have solutions that can't be kept in your head at any one time.

To put it differently, think of an algorithm that's constant time, but has a very large constant and an algorithm that's O(n). The constant time algorithm will be worse for small sets, but better for large sets (once n > that constant). That's the problem with teaching OO to people new to programming. You're adding an additional thing to an already difficult topic, and that thing you're adding doesn't really benefit you at that level of problem, but get to a bigger problem, and it starts to make sense.