Nature is cruel.

Why has nature allowed the evolution of pets?

Well evolution is the wrong word. Animals have always been there, but why did nature allow the survival of pets with high dependency needs?

Yes, their existence is sustained by mankind, as long as we exist they do.
For every dead pet owner dies a broken hearted pet.

Nature is cruel.

It has allowed our survival with our high dependency.
Our existence is sustained by the illusion of these dependencies being real.
The illusion of belief, love, science... the meaningless science to the why.