I don't have to worry about where the other person is; I can send WhatsApp messages to my family back in the US, or to friends here in the Netherlands, but it doesn't cost me anything. SMS to local numbers is free, but it's not free to send an SMS to the US

It's not free for me, granted you can get unlimited texting plans very cheap. But why bother for a service that won't even let you send a picture?