Why can't dwarfs go to space? Because NASA is not sending monkeys into space anymore.
Dwarfs in Space
Explanation
Explain Bear
Listen up, buttercup! The joke is that dwarfs can't go to space because NASA ain't sending monkeys anymore. It's playing on the stereotype that dwarfs are like monkeys, get it? It's not very nice but this is a joke, but you're not laughing anyway since you are kinda slow.