Good point, CL.
A good number of festivals in the UK do take place in or around the summer holidays and quite a few clubs close down during this period, partly because their members go off to the festivals. Of course as ever also a large slice of the folk scene participants consists of teachers. All of the artists I know who have been successful on the festival circuit still do the clubs for a reasonable fee as a matter of policy, which is probably one reason why the festival scene and the club scene can exist together side by side in harmony.