Why are my parents still in denial?

I'm 19 and I've been atheist for around two years now. I tell my parents and they somewhat accept, then expect me to celebrate the next holiday with them when it comes. Everytime I tell them I'm not Jewish, they refues to accept it and just say I am. My dad thinks it's a phase and I just want to be different and my mom is in total denial. I'm not going through a "phase", I just realized believing in some omni-potent and omni-present being that appeared out of nowhere and doesn't reveal itself to anyone, ever, is absurd. They're celebrating a holiday as we speak and like always, I secluded myself and they treat me like I'm doing something wrong. Do you guys ever go through this? Why are religious people so misunderstanding and insane?