It is far harder to get traction to reach their scale than to make money from your users when you have so many. They explicitly are focusing on growth.
Yes, focusing on growth to firmly establish their brand as the go-to phone-to-phone sharing app. Network effects will help them keep that position once they attain it.
Also focusing on user engagement, as they are narrowing down on solving needs that are a) painful and b) frequent. They want users they've already attracted to be firing up the app daily, not weekly or monthly.