Trouser-related astonishment

I bought some Ethical Trousers on Ebay. They were supposed to be 'one size fits all' without being elasticated (which is not truly one size fits all, more 'can you squeeze through this elastic band') and I must confess that one reason I bought them was to see how this could be true.

It is true! They sort of fold round you in a vaguely Japanese manner and tie off.

Why are more trousers not made in this cunning manner?

Also they are peacock blue. I like peacock blue.