Why is my hair still greasy/oily, even after washing it?

Admittedly, I don't bathe nearly as much as I should (depression + just not liking having to see my body + no motivation for literally anything lately), so maybe that's a part of it? I don't know, it's just frustrating. I have a habit of running my hand through my hair, but it's pretty frustrating that I'll end up with some oils or grease or whatever on my fingers, which ends up on my phone screen no matter how much I wipe my hand off...