Because in all of the posts that people get up in arms about (killing stuff with a .223 and scope drops) all he really does is post up pictures and a write up of what he found. Nowhere in those posts does he state an opinion. No "I thinks" or "I feels", just "this is what I observed and here are the pictures to accompany my observations". Those are facts.
As for "if you don't agree with Form, it is opinion", that isn't the case at all. If you do the work, and post up your findings in an objective and unbiased way, then it isn't opinion anymore. If you post up a "Well, one time, at hunting camp...", then it is nothing but an anecdote and can't be taken for fact.
Again, my experiences in some cases don't always align with what Form has found. For example, I have a Tract Toric UHD 2.5-15X44. I have had it mounted on 3 different rifles now. I have performed the drop test with it. Mine has not had a zero shift yet, unlike the one that he tested. Does that mean his findings were wrong? No, it just proves the point that he clearly lays out that he is testing a sample of one. As am I. Mine worked, his didn't. Take it for what it is, not what you want it to be.