If i'm sitting in a restaurant with friends, I'm not going to ask each of them for their email/paypal IDs so I can charge them when you can already get that info in venmo.
* Paypal did not integrate with facebook (does it even do that now?) so I would have to manually ask each person for their paypal id. Not fun for casual dinners with new friends
* Paypal was not free (they charged for debit or credit)
* Paypal did not have a good mobile UX
I remember this because the reason I adopted Venmo was because my roommates were searching for a solution to split rent and we looked at Paypal and ended up choosing Venmo. Then I started using it for social activities (restaurants, taxis, bars, etc.) and became an active user. I actually have had Paypal since the ebay days, but I never use it.