The loafer in the short trousers

Summer in Hong Kong is, as you may imagine, hot and sticky. As a result, I usually wear shorts to work. Until now that has never been a problem.
However, having just been given a promotion, I have been told to stick to long trousers from now on, otherwise those I work with will “think it is a party”. Bear in mind I never have to meet anyone from outside the office.
It doesn’t bother me particularly, but, seeing as I was interviewed for the new job in a scruffy pair of jeans and succeeded without comment, it strikes me as a bit narrow-minded that a smart, clean pair of shorts is considered less professional than jeans that have seen better days.
Why is that so? What’s wrong with a bit of leg on a man?
Is it a widely-held perception (conscious of subconscious) that short trousers somehow equal unprofessionism?

Moderator’s Note: Moving to IMHO.

I so want to work in a place where wearing shorts in not a problem! Any chance your office is looking to hire?!

So wear a skirt.