Multiple PicoSure tattoo removal sessions with zero progress?! Any thoughts on why I’m somehow immune to the laser?

I have 2 small (1x1 and 1x2) tattoos above both of my elbows. Both are all black. I’ve now had 4 sessions with a PicoSure laser to remove both, and they look like virtually nothing has happened to them. I’m so upset! My laser tech is very knowledgeable and has been experimenting with the settings to see if we can somehow get the ink to start breaking up. Any thoughts on why I’m somehow immune to the laser? Is that even possible?! (I’m in my early 20s, healthy, and the tattoos were done professionally)