Thinking back, the only time any clothing I purchased came in a garment bag (even an inexpensive disposable kind) was when I purchased a sport coat or suit. I wouldn't really expect a kilt to be supplied in a garment bag.

Maybe people have different expectations depending on where they are from.

Most of the kilts we sell at museum are shipped out, but for those picking them up in store they either usually wear them out, or we carefully fold the kilt and give it to them in a shopping bag to carry home, with verbal instructions on how to hang it once they reach home to avoid wrinkles. Never had a single person ask for a garment bag.