Professional attire

Piercings, tattoos, and hairstyles (including colored hair) are the main things I’m focusing on. I know some jobs don’t hire people if they can’t cover their tattoos, have colored hair, have certain hairstyles, or facial piercings (make you take it out.) I’ve personally experienced this when I was sixteen applying at six flags and didn’t even get passed the group part because of my colored hair. Personally I don’t understand the issue with these kind of things. Especially when I see people like Ms. Delauro in a very professional setting with purple hair. What do y’all think about it though? What are some legitimate reasons to not hire someone who has body art and different hair?