As Melanie mentioned, it's because this person was born over 150 years ago. Since WikiTree is a shared tree, we can't have our ancestors locked down from others' edits.
I'm curious why you want to change it. I see that another WikiTreer recently added some sources to that profile, and then that edit was reverted. I'm no expert on this family, but that edit didn't look like anything that would need to be reverted. Is there some controversy I'm missing here?