Do they really? Only one of those they created, the others they bought after they'd already become the most popular apps. You don't have to have any ideas to just measure what's already popular and buy it.
They built Facebook and Messenger from zero users to billions. Instagram had 50 million users when Facebook bought them. WhatsApp had around 300 million. Now they each have over a billion.
I wonder if they've found a "local peak" of knowing how to get people addicted to news feeds and updates for advertising purposes. Are they really trying to figure out what people want, or just what they can monetize that is similar to what they already do?
I agree with the broader point, but Facebook owns three of the most popular apps in the world. They have at least some idea of what people want.