Agree 100%! I looked all over for a marriage-able Khajiit or Bosmer for my characters to marry, only to be sadly disappointed.
I gave up on this happening. It seems like they just don't want to do this. I'd like a third Khajiit follower, though, so there can be four Khajiits in the Blades, including my character.
Pretty much this. From what I've read, Bethesda claims that it basically violates their lore to do Bosmer and Khajiit options for marriage, stating that the races don't usually get married (which is something I haven't seen much reference to in the lore), which sounds like horse feathers to me considering that they do have married Wood Elves throughout the series, and the fact that I've never seen anything that specifically states that Khajiit do not marry.
It would be nice if they did add marriage options where none currently exist, but they don't seem to have any interest in doing that at all. They so far haven't even added any new Khajiit or Argonian NPCs in the DLC's with any new voicework, and I don't even know if they even bothered adding any new dialogue for Shahvee, Derkeethus, and Scouts-Many-Marshes that other spouse options got added in through Hearthfire. They seem to be mainly sticking with NPCs that can use generic cross-race voices.