Because it works best for me is the simple answer, but I'll go more into detail with it. I am a student, even if I am taking a semester or so off, and I like the fact that it came with Microsoft Office for free. That isn't all, though, because I also have Pages for my iPad when I was using it more (and didn't have the RT). The next thing that I like, that I use a lot, is the combined kickstand and keyboard.
Let's get something straight.
There are plenty of keyboards for the iPad. I'm not debating the usefulness of the iPad for plenty of people. If it works amazingly for you, then you should continue to use it. These are all tools, computers that is, and you should choose the one that works best for you.
That being said, I have not found a keyboard for the iPad that is as good as the Surface RT's Type Cover. It's a joy to type on, much better than the main keyboard I was using on the iPad. Maybe it's the fact that the iPad isn't as long as the Surface, I'm not sure. The keyboard just doesn't feel as cramped, at least not to me.
Then we get to the next aspect that I like, the screen. It is a much better screen than the resolution would fool you into thinking. I would say that the screen is slightly better than my Macbook Air's, really, and my Macbook Air is better than any computer screen I had seen before it. The aspect ratio is also good for watching episodes of Dr Who.
Of course, this thing isn't without its flaws. Some people just can't seem to get their apps right. Apps that didn't lag on my old Nexus 7 (I had one, screen got cracked) lag a little on here. And I know it isn't the SoC, because I can play GAMES on it but can't get a lag-free experience with the KINDLE app. :|
Anyway, I could rant and rave about it's flaws and good sides for hours but you didn't ask about that. You asked why I prefer it, and I believe I laid out my personal use case on why I do.
