The stories in the first couple of pages of the rules are pretty awesome.

I'm wondering why there are no books in the TI universe.

Probably because Mr. Peterson is busy with too many other projects to have time to write anything.

As to other writers picking up the pen and doing TI fiction: there's simply not enough background info to base a first book off of. Don't get me wrong, I'd LOVE some TI fiction but I simply don't see it " in the pipe"