I think its more to do with the quality of some of tracks & the knock on effect it has on the racing. They should mix the tracks up a bit size wise as well, why the the World Champion only have to be good on big fast tracks ? ... maybe its because all its they have in Poland!
If I could pick places to have 10 GP's I would go for ...
KIngs Lynn, Peterborough, Sheffield, Monmore Green, Arena Essex, Coventry, Somerset,Eastbourne, Ipswich, & Rye House .... & I am talking trackwise, not capacity, parking, facilities etc ... just on decent race tracks