It's a design choice in this game. Adding an extra angle to a sex scene takes a small to moderate amount of time (though it can add multiple days of rendering to my schedule). Adding an extra position takes a huge amount of time. I decided early on to keep most sex scenes short and focused, instead adding more variety through multiple sex scenes with each character.
But you make a good point in that this is a character with a limited time span in which she appears in the game. There won't be many sex scenes with her. I might consider expanding that scene later (much later) for that reason, but it's not a priority.
If I were to put a number on it, I'd say an average sex scene with one complex position, or two simple positions, takes me about two weeks to pose, render, write, code, and test. For each additional position you add to it, you could probably add at least 3-4 additional days, perhaps even a week. It's easy to underestimate the sheer amount of work involved in this kind of thing, especially when I'm not doing this fulltime.