OG Xbox took so long, because most of its exclusives were also available on PC. Halo 1 & 2, for example. So there wasn't much interest. Developers focused on more interesting systems like the PS2 and the GameCube at the time.
> most of its exclusives were also available on PC. Halo 1 & 2, for example
While I agree with your point about most Xbox "exclusives" being available on PC as well, Halo 2 didn't arrive on PC (Windows Vista only too iirc) until 3 years after the original Xbox release, which was after Xbox 360 was already released and in full-swing. So I think there was a bit more to it than just lack of interest. Especially considering how massively popular Halo 2 was.
Consoles usually get working emulators well after their generation ends. Recent Nintendo consoles are an exception to that rule due to their low power compared to their competitors.
When Halo 2 was released - it was too early for a working emulator to be developed. Back then PS2 and GC emulators also weren't working properly yet. Though they were better than xbox emulators.
Also OG Xboxes were cheap and trivial to mod including converting in to debug consoles, so the homebrew community that often drives emulation didn't have as much reason to care. They could just install a debug BIOS, find a copy of the XDK floating around the ol' interwebs, and have basically the same toolset commercial game developers had.
Now that unmodified OG Xboxes are being irreparably damaged by failing clock capacitors and the used market is drying up as a result the people who still care about the platform have more reason to want a good emulator.
