Why is a sportswriter's gender an issue?

We shut down comments on the UCLA blog last weekend because things were getting downright nasty.
A couple of readers were threatening to fight each other. A few others were taking shots at reporter Jill Painter for an innocuous post about running back Kahlil Bell perhaps getting the chance to play with Brett Favre with the Minnesota Vikings.
What bothered me was that some readers felt the need to bring gender into the equation.
No, Jill didn't play wide receiver in college. Does that mean she can't report on football? Does that mean we shouldn't send a male reporter to cover a Sparks game?
I've often thought some of my best stories were on sports I wasn't familiar with, as I had to learn about them and convey that information to the reader.
One look at me and you'd think I was an offensive lineman in high school and/or college. But I've never played a down of football in my life. Probably wouldn't even be able to figure out where all the pads go. But I've covered plenty of football, including the NFL.
I was standing next to USA Today reporter Denise Tom the day Cincinnati Bengals coach Sam Wyche decided to not let her into the locker room. It didn't hit me at the moment -- I was a cub reporter worried about meeting my deadline -- but later that night after filing my story I stopped and thought about how Wyche prevented Tom from doing the same thing I was trying to do -- my job. That incident occured nearly 20 years ago. We've come a long way since then.
So why is gender still brought into question for female sportswriters?