Because the government has the extra money to spend on fish sex changes.
Check it out:

The National Science Foundation has awarded a total of $727,798 in federal funds for a three-year study on the impacts of size-selective mortality on sex-changing fish.

“Many marine fish species change sex during their lifetimes, and many of them are targets of commercial and recreational fishing,” the grant said. “The timing of sex change in these animals is often related to body size, so populations typically consist of many small fish of the initial sex (usually female) and few large fish of the other sex (usually male).”