I'd bet it is because of the other solutions that would have rendered those tools obsolete in no time at all.

You only need your bare hands to fulfil the necessity to gather flint and stone from the ground. Trolls can break boulders for you including copper and tin veins. And the antler pickaxe is easy to access within the first or second hour for repeat players.

I have little doubt that it would be easy to implement them, but you don't want to confuse the newbies with more items that run out of use in less time than it takes to acquire them. *cough* bronze equipment *cough*