It may well be the way companies sell package holidays, they all used to go on certain days (hotel ,changeover) but now people want to go the days that suit them so instead of all flights going on a Wednesday they are now 5 flights a week and people picking say Easyjet out and return on Jet2 because of days of operation, times etc.
The other thing 30 years ago the main small aircraft were a lot smaller than now (1-11, B732) as against B738/A321 even A320 are not common.