Where they really get you is the FOMO factor when a banner is about to expire and you have lost your 50/50. I wonder how much of their revenue comes from the final 24 hrs of that countdown.
Probably some, but I think it works more like the crowdfunding model. The first few days of the banner has the biggest spenders go hard, and then it cools down and ramps up slightly by the end. The former is going to include a lot of spenders going for 6 copies, so they are much less elastic in how to optimally spend on the banner.