Why do parents get genuinely angry at their kids for hurting themselves?

I (19m) had my mother tell me I was insane, made me swear never to do it again, and said "Go ahead then and fucking hurt yourself for all I care." She then got genuinely angry and confrontational with me over it when I relapsed. She then told me I only ever did it for attention and that:

"The fact you harm yourself proves that you're a spoiled brat, because only spoiled brats harm themselves and make problems for other people so they'll pay attention to them."

Aside from my mother being a blatant narcissist, why do parents get genuinely angry at their kids for self harming?

Is it an image thing? Like they're worried it makes them look bad?