We're a little sad about this one, but we suppose that it was an inevitable consequence given how technology has progressed. Thirty years ago, it was customary to send a postcard to friends and family when you were on vacation. The postcard usually had a picture of wherever you were staying, and a message to tell them how much fun you were having. It was a little strange, but it was cute in its own way.
It just isn't necessary now. All your friends know where you are and what you're doing every day, because you put it on social media. When you're on vacation, your Instagram account is full of pictures of your face, with famous landmarks in the background. You can send messages to whomever you want, whenever you please. Postcards are quirky and archaic - but again, millennials are being blamed for a consequence of technology!