Well, I guess it's a free world, so in theory (and in practice) just about everybody can go and organise their own symposium. The proof of the pudding will be in the eating.
As to why, I think it'd be best to ask them directly. Not sure you will get a reply. I tried to contact them, and did not get one. Whether that is because they are too busy, or because they are not keen on talking to AWGB members, I do not know. Since John (BHT) is one of their demonstrators, maybe he can shine a better light onto that.
From what I have seen so far, I don't think that the two events are really comparable. UKIWS is selling a maximum of 30 tickets for their pro demos, and there is only one venue for these. This is a much smaller event, and maybe that's just as well.