It was designed for Venmo to prove to new users that the app has a large network and was trustworthy

> Yeah, absolutely, so one of the biggest purposes of the social feed when Venmo first launched was around this concept of social proof. So if you think about a product like Venmo, it’s really only useful to you if people that you want to transact with are also using Venmo. So when Venmo launched, we had two feeds, we had the public feed and the friend feed. And immediately when a new user signed up for Venmo, you could see in the public feed that Venmo was something other people were using.

From a Venmo product lead - https://www.theverge.com/2017/11/14/16643192/venmo-stalking-...