That's a good question. There have been many explanations and theories for this. There are some that always use the lame and over-used excuse "every good game has a PC port". Whether that's true or not, there are some games I'd rather emulate than have a PC version of (Halo is a good example so I can play Co-op on my laptop). I can think of many Xbox exclusive games worth emulating as well (we get requests for JSRF alot). Other excuses are "there were no good game for Xbox", "just download games and play them on your hard drive (which defeats the purpose of emulation)", "there aren't enough RPGs", and the list goes on.
There are some emu authors that only work on these emulators for the recognition (sad to say that what it looks like to me). When you're an Xbox emu author, your work doesn't get appreciated much. I really don't care about popularity and stuff like that (this isn't high school, dammit). TBH, I could care less that I'm the only one actively working on this (as I prefer to work alone most of the time). I love Xbox1 with a passion, and I'm willing to do what ever it takes to see it emulated! The thought of emulating all of those complex chipsets puts a cheezy smile on my face

So in the end, I could care less what game has a PC port, as long as that game works, it paves the way for more games to be playable. Thanks for your appreciation!