Actually, I don't disagree with you. The general rule is that unless the information is of a sensitive nature or would harm the individual then one should try to get information on-the-record.
But the lines have blurred now, and sports journalism is more into gossip and personal issues than on-the-field issues.
There was a time when journalists didn't care if TO was a "locker room" cancer, so there was really no need to rely on unnamed sources because that stuff wasn't newsworthy.
But now because we're in such an entertainment, I-need-to-know-all-your-personal-business, gossip-driven world, you get more stories like this, and reporters are more apt to use unnamed sources. And I think the rush to get stuff out on the Internet fuels a lot of stories that are just rumors and not really substantive. Social media reporting is more "feelings" than "fact" based, i.e., I "feel" TO is a locker room cancer. Story: Teammate says TO is a locker room cancer. He might not be, but when feelings rule the day, facts get pushed aside.
My beef, however, has always been that I don't think most reporters are "making up" sources. (Well, I didn't a few years ago when I had these debates with fellow posters. Now, I'm not so sure.) Granted, they might not be properly venting these sources, but there are standards (at least based on the newspapers I worked for) on how you use anonymous sources. And one of those standards was that you never use just one source unless that person is so close to the information, there's no doubt about its trustworthiness. Even then, you have to be aware that you could be the one being used even by a credible single source. But that's where your relationship with the source comes in.