Why are teen moms judged so harshly?

Why do people assume that just because someone is a young mother, they aren't capable of being a good one. I know some teens aren't close to being ready, but some can be really good moms. And just because it happened when we were younger doesn't mean we dont deserve support and deserve criticism. It really bugs me and makes me ashamed to be pregnant and tell people. I dont want people having thst opinion of me, I've always been known as the good girl over achiever, and yeah I hated being labed as thst, but its better then being labled as a slut, who Is ruining her life and a childs. I know I made a mistake and should have been smarter, but I'm not ruining anyones life. Babies are gifts, they dont ruin lives, yeah it will be harder but, my life is not ruined.