Why are parents so against sex talk?!

I’m 18 and all of the things I learned about sex were from google, if I asked my mom which I did many times she would say to wait until I’m out of college, and it makes me mad. I hear all these stories were moms help you out, I wanted to tell my mom when I lost my virginity but no because when I did try to tell her she said I better not be doing anything bad. It makes me upset that some parents believe that not talking about it’s the best. I wish I knew all the contraception options from the beginning, all those months freaking out about me being pregnant, I was denied by my mom to take birth control and she even still thinks I’m a virgin. And the worst part of everything is that I don’t think I can ever tell her, I can never trust her or ask her questions about things that I need to know. Why do parents do this? Like I’m sorry, But why do you let your full of hormones child go out in the world with no information about something so important?!?!?