Dave is correct.
The Top bands are controlled entirely by the top promoters and Management Agencies.... in turn they are tied in to the top traditional venues around Britain, (Hammersmith Odeon, Manchester 02 arena etc) ... its like a circus, a mafia if you like, where I am certain that financial incentives change hands to maintain things that way. After all, a lot of dosh is involved.
Some of the top promoters think that one gig in Wales (Cardiff) is sufficient for a tour ... and we all know that is ridiculous.
On top of that, many top acts are prima donnas, and can veto many venues for personal reasons.
Several top acts have openly stated that they don't like playing in Llandudno, or don't want to come here.