Originally Posted by redknob
I'd say it's a comprimise between getting value from his weaker/drawing hands and not owning yourself when he does turn up with the 9 or better.
I think it's mainly to keep his calling range as wide as we can, while extracting maximum value.
If we raise to pot here, his calling range is reduced to basically 9's only, and this crushes our equity vs. his calling range. When we raise small here, we keep his calling range super-wide and our equity vs. his calling range nice and big.