I think that the reason behind this block-unblock cycle that reliance goes through every time a movie of theirs is released is quite simple. They do not want to block these sites permanently because then they lose an edge in the competition with airtel.

On the other hand whenever a movie from Reliance entertainment comes out they want to avoid the cams to spread for the first few weeks so they block these sites. Once the first couple of weeks have passed they undo the blocks.