They all evolve until you can text people on them.

Instagram’s co-founders, Kevin Systrom and Mike Krieger created a mobile social network based on visual storytelling. The impetus provided by the early photography-centric approach turned it into a fast-growing phenomenon. For Facebook, it was an existential threat. And it was worth spending nearly a billion dollars to own, control, and eventually subsume. And that’s precisely what Facebook has done.

Source: Instagram is dead – On my Om

As stated by Zawinky’s Law:

“Every program attempts to expand until it can read mail. Those programs which cannot so expand are replaced by ones which can.”

In the age of social media I suppose email is passé, so apps expand until they can do what every other social media app does