I pick my scabs on my skin what are reasons I can't stop?

Skin picking. Skin-picking is a type of self-injurious behavior involving the pulling, scratching, lancing, digging, or gouging of one's own body. It is associated with social impairment, and increased medical and mental health concerns. Specifically it is often associated with anxiety. One type of anxiety disorder call obsessive-compulsive disorder. It is treatable so an evaluation would be a good start.
Anxiety? Are you under a lot of stress? That is a very common reason why someone would pick at scabs. Seek help.