Yeah, it's actually kind of low. Kindle Direct Publishing takes 30% of digital book sales and those are like a couple megabytes. Steam is distributing 100GB+ titles on top of adding Steamworks SDK and a ton of other features.
Similarly, when Steam launched, its biggest competitor was retail. Studios got paid a % of the wholesale price (after the publisher recovered its costs), which worked out to an average of approximately 10-15% of the retail price for successful games and 0% for unsuccessful games. (Note: this does not include the milestone payments to the studio during the development of the game.)
But markets have changed. 30% may or may not be a great deal anymore. (For KDP, many authors say that the 30% is worth it because the volume of their Amazon sales dwarfs all other-channel sales combined. Some relatively famous sci-fi authors have said that about 90% of the sales of their self-published works were through Amazon.)
You can buy and play games on Epic store, it works just as well. It has achievements too. Devs get a larger cut.