Seems no rhyme or reason for the increase on Friday.
I read an article that Friday and Saturday nights have become popular for one-night party nights where people rent a room for one night and have a party there (and sometimes trash the place), so they don't have to clean up the mess. I guess the hotels just figure it is easier to pass on their added expense to everyone rather than trying to recover damages from individuals. When we were in St. Louis chasing the 4014, a party like this was going on across the hall from us in our hotel (and the hotel was in a nice area). It was a kids party, and the parents spent their time in the bar downstairs. When it got late (and the noise level did not go down after multiple requests from hotel staff), the police were called and one of the parents ended up getting tasered. It was not pretty.