The short answer is because that content hasn't been written for them.
The longer answer depends on the character. Some characters don't have certain kinds of content because that's just not the fetish that they're intended to cater to. Not every character is designed to fill every niche, because they need character, and that comes from what they don't do as much as what they do. And some of them don't have certain kinds of content because it just hasn't been written yet, but will be written eventually.
To answer your specific questions...
I don't want to speak to Bubbles' plans for Quin, but I can talk about Elyon. The broody elf isn't designed to cater to people who want to top men. He's designed to cater to people who see damaged, misunderstood pretty boys and want to save them, and also who want to get fucked into the floor, led around with a leash, put in a cage, etc. in the process.