Simple. Because if you are going to pay for advice, it had better be worth it. In the case of PBS, you have NO IDEA whether or not someone on the CAL forum really understands what they are talking about. The same holds true for the UAL forum. You are not going to be conversing with a PBS SME, that is almost guaranteed. However, if you go on Prefbid (which again doesn't charge for admission), you will be. What site would you trust?

Now Sleeves, since you are always on here looking for a hint of any CAL bashing from a L-UALer like myself, let me say this: The L-CAL PBS gurus, the ones that are behind Prefbid and have years of experince, are exceptional in their knowledge and desire to help the pilot group understand how to properly bid using the PBS system. Mike and George, two of the guys that appear in the video series, are two such examples. I've met them both, and walked away highly impressed and relieved to know that we all have the benefit of their high level of expertise and leadership with the PBS system.