The answer to your question (and similar ones) almost always has something to do with "keeping something for later".
Exemplary scenario:
1. Starlet appears in first video - interest waxes
2. Starlet is no longer new - interest wanes
3. Starlet announces first anal - interest waxes
4. Starlet stuffs her ass all the time - interest wanes
Interracial, Gang Bangs, Bukkake, etc.
It's all got to do with a girl's marketing strategy (or lack there of).
Now don't get me wrong - I prefer the "balls out" approach to a career. In reality, however, it probably shortens it.


