Kilts are moving towards being, not only formal wear, but everyday clothing.

Most people don't dress up every day, so kilt-wearing styles are reflecting that.

I think it's a good thing, since it gets kilts out of the mode of being only a formal costume (like a tuxedo).

What's bad form is to wear a dressed-down kilt outfit to a formal occassion. It's akin to guys wearing tennis shoes with a tuxedo or a tuxedo-print t-shirt instead of the real thing.