Why all the date ticket swapping hubbub? Is one day more desirable?

Confused why people want to swap so badly. The some guesses are

• People bought overpriced Sat and got cheap Friday. But these folks are selling not swapping
• Flights on Friday night, so Saturday is better. But many seem to want Friday?

Biggest thing seems to be Friday is “first” so people want to enjoy it before being spoiled?