Cookie based referral links are not perfect either, there is no perfect referral system (each have its own pros & cons), so combination of both was the best option to start with and see how people react. Until transaction referral system started getting abused, which has not happened with other distributions before. Maybe there is just more people with skills like that on Steemit.
Also, having users actually interact with the app showcases its features and helps marketing too, everybody now knows that transactions are fast, you can request for payment via chat and you can have smart-contracts that open in one year.