How else would you send money to someone across the planet if neither of you have bank accounts? You can hand WU cash and your recipient can get cash at the other end. "Just get a bank account" is not always an option.

I've never used Western Union, but if you want to send money across the world quickly, I'm not sure of a better way to get it done. Transferring a thousand dollars from my bank account to the bank account of a relative would likely take at least a couple of days. Just transferring from my online bank to my local credit union takes a couple of days.

(Plus as others have noted, not everyone has a bank account.)

Poorer people are the main clientele.

Amazing there hasn't been a single mention of transferwise in this thread