The main reason is that city states were becoming increasingly wealthy
The nation was not unified and every city was a state for itself. This meant that they didn't have to think about the rest of the land and they focused on trading and getting richer and richer. The rich lords and ladies liked art and employed numerous artists to do commission work or to make the state a better place or similar things.
England is a constitutional monarchy (with Queen Elizabeth II as head of state) and a parliamentary democracy (with parliament as the legislative organ).
