For an advanced course that is how the economics works out. They are expensive to produce and have limited demand, and typically only for a few years until they are replaced.

Professors making students buy the textbook they wrote for $200 is especially out of line.

In any other industry they call this corruption, but in academia it’s apparently ok.

Anna has an archive for students who can't afford books.

As an educator I always make a point to give the resources to the students and or give avenues to it that are not paywalled.

Knowledge is the only resource that only becomes greater the more is shared because people share back what they learned. Mind you this only works if people are paying it forward. But often the educator gets more from teaching than the student does.