I'm not saying 30% is justified, but there's a significant difference between the service provided by storefronts vs credit card companies. You're comparing Apple to oranges.
Having my app on a large store front such as Steam or Play Store can and often does bring a lot of organic views. I don't know any business getting organic views from credit companies, except the sponsored once, which I'm sure are probably paying a good chunk for that. App stores also handle feature development, hosting, and many other services. What do credit card companies give to business?
Now the question is, how much is the storefront traffic worth to you in terms of cut. If you get 30% or more sales being on Steam vs selling on your own website, then isn't it technically worth it being on that store front?
Having my app on a large store front such as Steam or Play Store can and often does bring a lot of organic views. I don't know any business getting organic views from credit companies, except the sponsored once, which I'm sure are probably paying a good chunk for that. App stores also handle feature development, hosting, and many other services. What do credit card companies give to business?
Now the question is, how much is the storefront traffic worth to you in terms of cut. If you get 30% or more sales being on Steam vs selling on your own website, then isn't it technically worth it being on that store front?