Why do so many summer dresses have long sleeves nowadays? ( lighthearted)

[malificent7]

I get that everyone hates their upper arms ( me included) but why do so many summer dresses nowadays have really long sleeves. Zara...I am looking at you and many other labels too.
There is a happy medium between spaghetti straps and long sleeves.
What is particularly mysifying is the long sleeve, mini skirt combo.
I like short sleeves or 3/4 sleeves ...humph!

Also why make summer dresses from hot sweaty polyester? I spy something nice looking then on closer inspection it's polyester. My heart sinks. Yes I know it's cheap (supposedly) but what a waste of time & effort.