It has nothing to do with the weekends, maybe it is just because some users of bitcoin are getting their payments at weekends, and they usually convert it to fiat to use it for their lives. It is also because bitcoin is not yet widely used in real life, in stores. And bitcoin's price dropping is because of the panic sellers who are afraid to lose money. Being greedy.
Look what happen to price in last few month every time when weekend start price is slowly recovers and every time is that same path.
Its not just that some are get payed usually is 1st or 15th but not so middle in the month.
As for greed this is something that is bound to us all people we are greedy and we will always be greedy and wanting more and more, its our nature.