Why do you think parents miss the warning signs of mental illness in their kids?

My mum caught me and stopped me from swallowing Caustic soda when I was 10 years old, she also found a barbed wired noose in my wardrobe when I was 14, I hid my depression back then and because of that my mum thought I was just “seeking attention” but I needed help let alone love that I was lacking from my parents, they didn’t even switch on that something was wrong when I took up heroin at 16, sold eccies at over age raves, getting into trouble by the cops all the time, then when she finally ransacked my room and found scrunched used sheets of foil (smoking heroin paraphinaelia) in my drawers, finding my knife collection, bullets. Her solution was to throw me out of home just two weeks after I turned 18.