so you find the same show/jokes over and over again amusing. lol

I don't know, either. I'm sure there are studies that show that guys watch TV on Monday night more than any other night, kids watch TV on Friday nights, women watch more TV during the day, etc. etc. If that's so (and I'm just guessing so don't quote me), you have to put your show that attracts the male audience up at that particular time, your kid show at a particular time, your chick show at a certain time, and your old people show at a certain time. Gotta get those marketing dollars!

I am not properly laughing, but I am still amused, I have happily watched each episode of Friends many times over

I think Mondays are important because it's the beginning of the week, plus maybe networks know that people generally hate Mondays and just want to relax and spend time in the evenings watching TV. Also, it gives them a chance to advertise their lineups for the rest of the week.