I take issue with your "correct" answer.

Q: Why do cows produce milk?

A: Because calves (baby cows) drink it.

May I suggest the one common in my childhood playgrounds as an alternative?

  How do you escape from a perfectly sealed room with a table in it?

  You run around the table until your legs are sore, use the saw to cut the table into two, two halves make a whole, you escape through the hole.

For people wondering, in some locations, sore and saw are homophones.

[deleted]

Yep, if the riddle asked "what do calves drink", then "milk" would definitely have been the correct answer.

Obviously. My point is that it's already not all that unreasonable, which you notably didn't address.