Because she's been begging for anything A/S that's remotely good. Not that I can guarantee this is remotely good, but it's buried so deep as a flashback in an S/X series that I'm almost sure I can guarantee she hasn't read it.
One of my two only ever attempts at Angel(us)/Spike smut. Very tame NC-17 that's more about the kink than the smut. Which kink? Oh, stop looking at me like that. Do I have more than one kink?