Why don't humans stretch instinctively like cats?

Fun fact, there is a name for the kind of stretching you see your cat or dog doing, it’s called pandiculation.

Here’s a cat pandiculating:

A lion:

A dog:

A horse:

An elephant:

A human:

Yeah, that’s right. Turns out the premise behind your question is kind of flawed because humans, and pretty much every mammal for that matter, share the same instincts to stretch as our cats. Pandiculation is actually a key function of our musculoskeletal system as it is a subconscious action that prepares our muscles for movement after long periods of rest.

EDIT: Because it’s come up a couple of times in the comments, here’s some PANDAculation for you all too.

…heh, see what I did there?