More than likely Valve has offered better deals to these larger companies to get them back in-house. It's very probable EA, Bethesda, Microsoft, etc. all have gotten more favorable terms now, by proving they were willing to leave Steam and roll their own launcher.
They might have even better deals, but at some point 20% for handling everything and supporting payments with potential of fraud, chargebacks etc. in nearly every country should start look like not horrible deal. Remembering what the retail margins were back in the day when they needed to make and ship physical boxes...
10 people in 4 years don't sound like a lot to setup and run support, distribution, payment integrations for let's say 100+ countries. Which many having unique payment providers.
