This question comes up here from time to time.
For me, it's always seemed a little foreign, because in my experience, the lectures were almost always valuable. I had one or two classes that felt like the professor was more or less just reading the textbook too us, but in most cases it was easy to identify the value added by the lecturer.
How many questions are you asking in each class? Or immediately after the class when you don't have to ask in front of everyone.
I know it's not always possible, to be this prepared, but in an ideal situation, you should come to class with having done some pre-reading about the material that will be covered. If you can, prepare a few questions. There's a good chance the lecture will cover them, but if it doesn't, then ask them, so that you understand and stay engaged with the material.
If all of your classes are just lecturers regurgitating a textbook you may be better off spending that time reading and working yourself. But this means that you (a) need to have the discipline to do that, and (b) be confident enough that the subset of classes you have attended is a representative sample of the entire course. Often in lectures, professors will give hints about what material exams will focus on, tell you what information in the textbook is out of date, or give you real-world examples of how certain material works. I never had the confidence in my own abilities to turn my back on this kind of thing.