Because the imagestation website designers are smart.
imagestation is in the business of selling prints and products with photos on them. It's arguably a risky strategy, profit-wise, to offer unlimited storage space to anyone, in the hopes that users will actually order enough products from them to actually profit on the cost of the server space used to store the images. One issue they found was images appearing in online forums. Any time anyone views an imagestation stored image, it is downloaded from the imagestation servers to the user's computer, and this takes bandwidth. Multiply the size of an image in KB by the number of downloads, and the bandwidth usage rises with each page view. When it gets into the GB for each image, it then likely costs a lot more to host the image than they're ever going to make in profits derived from that image. So they came up with clever code to prevent it.
Do yourself a favour, and get your own domain name and storage space.
www.inexpensivedomains.com will get you up and running at about $10.00 a month. You'll have your own unrestricted space and bandwidth and you can get started on an autoMATTic.com website.