I myself am one of them, but I attribute that to the fact that this is a graduate version of an undergrad class I took two years ago (but have to take the grad version for degree requirements). Instead, I've been skimming the posted exercises and assessing myself which specific topics I need to brush up on.

And not watching lectures is not the same as not reviewing the material. I generally prefer textbooks and working through proofs or practice problems by hand. If I listen to someone describe something technical I zone out too quickly. The only exception seems to be if I'm able to work ahead enough that the lecture feels like review. Then I'm able to engage.