Um, because it is not a camera?
Well, it is not a phone, not a radio, not a tv, not a computer, not a notepad, not a bookshelf, not many other lots of things, but we use it to take pictures, make calls, whatch movies and listen to music, take noter etc...!
The point is that it's odd to have a built-in app, or tool, that's called "photocamera" and not using it as such, or not considering it to be really meant to be a camera, just because the device itself it's not a camera!
There are many humorous things or even ridiculous, that we can do with our iPad and its bizarre apps (for example the mirror app to adjust one's makeup!!), and the camera is not the funniest, in my opinion. Again, a mobile phone is not a camera, either, still it comes sometimes with an impressively good camera, with an incorporated flash. For these reasons it's quite simple to agree that what looks obvious for you, probably it is not for other people who have a wider sight on things.
I agree that the no-flash decision made by Apple is more on a technical side of things: it may demand too much (battery? precision? physical room?) for how the ipad is conceived, and the price it can cost, compared to the previous editions, and other apple devices. So they greatly improved the camera and let it without a flash also in the ipad 3. A step forwards.
Fra