I have had the same problem at other places. In fact, last week I ordered a fish eye box from a web fly shop. I was auto charged via credit card. I kept asking for shipping confirmation. My emails were not answered. The phone went to voice mail. After nearly 2 weeks I was notified that the item wasn't in stock and Amy credit card would be credited back.
It is very irritating.
It is not a computer thing (they can keep track of inventory better than a person). It is not a person problem.
It is a business problem. Having a passion for fly fishing/fly tying doesn't mean you are a businessman. It doesn't give you an MBA, doesn't teach you accounting or even business principles.
Again, my experience was not with Mariott's, but a different "store".