What, you expected them to actually show you the yearbook where your uncle is drunk at the wedding? They only hand out the pages where everyone's smiling nicely. It's way easier to test you on dates and names than on why things actually fell apart.
Yeah, it bugs you because it feels dishonest, right? Been there. What worked for me was asking the teacher after class, one on one, for their take on the skipped stuff or a book that covers it. Sometimes they just run out of time and will point you to the good material.