Here is the fee schedule:
-30% Purchased Coins
-0% Earned Coins
-15% Tipping Fee
So if someone buys 100 coins and gives you 100 coins, your actual take home coinage is 55 because 30 coins went to Google/Apple and 15 coins went to Tapas. Google/Apple charges 30% fee to everyone who uses them, whether Tapas or Pokemon GO. This is also why Costco can sell Google Play and iTunes cards for 18% off face value, because there's still 12% margins.
Meanwhile if someone earns 100 coins (via watching videos) and gives you 100 coins, your actual take home coinage is 85 because 15 coins went to Tapas.
15% may sound like a lot, but consider that Tapas has 6+ months of developer time invested into the program, plus server demands, ongoing logistics of having an ad network, processing payments to creators, etc. All of that requires making payroll. Tapas also had to acquire the capital to start through preferred funding so it could get the program going and has to repay that. Plus, Tapas is pouring a lot of the money back into developing more features and marketing themselves, so that creators can get even more tips. There is one staff member who is solely dedicated to growing the site. His title is Senior Director of Growth and he's hard at work behind the scenes doing what it takes to make sure Tapas grows more and more each month so that creators here can have a bigger and better audience.
The 15% fee is money well spent.