I wish more authors used leanpub/gumroad and the likes. But these sites are nowhere close amazon's popularity, not to mention amazon has reviews and these sites

I wish more authors used leanpub/gumroad and the likes. But these sites are nowhere close amazon's popularity, not to mention amazon has reviews and these sites have only ratings or not even that. If authors aren't using Kindle Unlimited, then using such sites and pushing it to their readers on social media (might even offer lower cost because of higher earnings) might atleast be a good start.