You're completely missing the fact that they established themselves as a trusted e-shop, with consumer friendly policies, in a day before people trusted PayPal. It had a lot less to do with 'not wanting to click setup.exe' and more 'Mom trusts Steam because her coworker told her it's safe' to a generation of kids without CCs.

I think Roblox, Minecraft, WoW, LoL, and Fortnite all prove it's fully possible to operate outside that closed platform and see success, as well.