This question crops up quite a bit here, and I'm curious about it myself. A few people have mentioned the fact that your story is a .PDF, and that might have something to do with it, but I've had downloads into triple figures on things that were just ordinary text. I can only assume that it's got something to do with making it easier to read--"downloading" non-PDF literature just brings up the text in a new page, and I can imagine it being much better for people using smartphones. When browsing dA on my kindle, I use "article mode" to much the same effect (though I very much doubt this counts as a download on the site).
One thing I feel it's really worth mentioning is that, even after three hundred and something downloads on one particular deviation, I can't find even one stolen version of it anywhere on the internet. If people wanted to steal it, I can't help but feel they'd just copy and paste right from the deviation page. Even if that was impossible, they could simply type a copy. Downloading literature is, from an art thief's point of view, utterly pointless.
Also, as *merrak says, there doesn't seem to be a great deal of theft going on. The closest I've ever come is somebody offering ten copies of my POD paperback for sale on eBay, even though I know they don't have any. I can only assume that, should anybody buy one from them at their excessive price, they'll buy one from Amazon/Createspace and then pass it on. Kind of dodgy, probably against eBay's policies, but frankly not my problem.
Usually when I end up downloading literature on dA, it's so that I can read it later (if someone has asked for a critique and I'm not around at my laptop/internet for a long while) or to just see it better at times. I doubt the majority of the time it's for "stealing" your work.
However, if you're paranoid about people downloading your writings, there is an option when you upload deviations that you can uncheck so that people can't download it.
It is a pdf. Those are basically designed to be downloaded and read on devices. If the reader has poor vision there is probably no other way they could read the work as I don't think DA supports resizing pdf text or text-to-speech.
Right, which in general would be guaranteed-A essays. Or work that is already known to be successful, so honestly famous people are more likely to be plagiarized off of. At the least they have to find your work.
When I try to load your first chapter, it gave me an error (don't know why, but it did and it has been doing that on a lot of PDF stories lately.) But after "dowloading" the story, it showed up just fine.