Why Instagram add Instagram Stories

Instagram Stories will eventually be Snapchat for the masses. Easier to understand and your social network is already there. 

Vine already become irrelevant because Instagram Video, will Snapchat be too? 

Why Instagram do this? No. of post photos and more user interactions. While now average Instagram user probably post 1-2 photos daily, Stories encouraged users to post more without worrying what their followers think.

More Posts -> More Interactions -> More Time Spent on App -> More Money

However I still don’t get this whole “ephemeral” thing (your Instagram Stories posts will only last for 24hrs) why not give an option to make it permanent and post it to public?  ???