Why does it always take so long for this vendor to mail purchases?

I've purchased sports bras from this vendor on three occasions, and every time I think there must be another vendor who can deliver this item sooner. It usually takes at least a week to receive a notice that the item is about to be shipped, and then it sometimes takes 4-5 days to get to California. It seems to me orders should be able to be shipped within 24-48 hours of the online purchase. The bras themselves are great, though the underwire came out of the last one I purchased and it's impossible to get it back in.