WHY DONT THE GIRLS WERE LONG DRESSES IN THE 5TH SEASON AND SO FOURTH?

I think it was because once it became the "60's" short skirts were in fashion, especially with teenagers. I guess it depended how old you were back then. Joanie & Jenny wore short skirts, Marion stuck with the long ones...and Lori Beth started wearing hot pants. So maybe different things were fashionable for different age groups.