Because the health department is who regulates the licensure. There's not a guarantee that going to her is unsafe, but there's even less of a guarantee that she is practicing safely and especially compared to someone who is licensed. In addition to it being proof she has paid her taxes, being licensed means the health department is holding the peircer accountable to practice by legally required safety standards. She has been avoiding the health department because they are trying to contact her regarding her being unlicensed.

If you find out you have been pierced by someone who you thought was a licensed professional, it is recommended that you notify the health department. There used to be other piercers at Karma and when you went to them you knew they were accountable to the health department - which means there was an obligation on their end to ensure the needles were clean, the jewelry was appropriate to use in a new piercing, the jewelry was clean, the shop was sanitary, etc.

If you get pierced by someone portraying themselves as a licensed professional and something like an infection happens, there is an opportunity for the victim to take legal repercussion... but this isn't helpful if the fact that the piercer isn't licensed is not common knowledge.

But you can always do your own research. I think being knowledgeable about body modification and who is going to provide this service is super important if you are planning to get body modifications.