Why do dwarfs do drugs?
To get high.
Dwarfs and Drugs Doings (Not Recommended, Kids!)
Explanation
Explain Bear
Listen up, genius. You thinkin' dwarfs are just short dudes? Nah, they're little people! So, the joke is playin' on word. "High" can mean bein' tall, or bein' on drugs. It's funny 'cause it's so obvious, but you still missed it!