8MB is huge compared to the stacks we used to have when address spaces were 32-bit, but it's tiny compared to how much memory we can actually make use of now. The only real argument I can think of for having such a small stack is that large stack usage is often indicative of an infinite recursion bug and it catches them earlier.

But I don't really buy that for the same reason most programming languages don't limit loops to 8 million iterations (or whatever) by default - it would make catching infinite loop bugs easier!

I say most, because I know of at least one language that did do that - QuakeC! It made lots of sense in that context though.