It was my Mums way of keeping control. She likes to be the one "in the know" that the family turns to because "Mum will know". Dealing with her was the worst part of my cancer experience, she actually told me off multiple times because I was saying she couldn't tell anyone, and she was telling people before I was even properly diagnosed.
That was 3 years ago now, I just had a nice walk with her (and Dad) for Mothers Day. Life's too short to be angry with them. Focus on what is important at the moment, and that's you.