These arguments are being made by a tiny minority for the benefit of a small community of techies who already have platforms available to them that work they way you want and take advantage of it, like you do. It's like coupon clippers insisting on a law that all products sold must some with discount coupons.
Minority? Probably. Tiny? Absolutely not.
Here [0] is a breakdown of 70 popular Steam games by the source of purchase for their reviewers as of a year ago. About 28% of all Steam purchases happen outside of Steam itself, with Valve getting a 0% cut. Note that for many games a majority of reviewers did not purchase it on Steam itself.
0: https://docs.google.com/spreadsheets/u/0/d/1ICv-UE4i651yMkpD...