the reason for that is because steam isn't just a launcher. if you don't use steam you might think so, because giving you a play button, managing downloads, and maybe tracking achievements is all other platforms do. steam, on the other hand, is an entire toolkit built to simplify everything in gaming -- whether what you seek is community spaces, a workshop to easily install mods and other community content, one-click linux compatibility, in-home streaming, easy game invites and in-game chat with your friends, or a plethora of other features, buying on steam vs non-steam is usually a massive difference.

i bought gta v on disk back when it released, as opposed to my friends who only joined a few years later and had the bandwidth to just buy the steam version and download it, and whenever we played together they just had so much of an easier experience.

the reason steam's user base is so loyal is because steam provides things that actually matter to them, and valve spent decades ensuring that they provide the best damn experience possible. epic games, on the other hand, had one surprise success with fortnite, and decided they want the game store market to turn it into a long-term revenue stream, but what they forgot to consider is to give people the same experience steam provides. egs has a fundamentally selfish design, it literally only caters to epic and only does the bare minimum for anyone else.

so if your proposition is that people should ditch that platform that goes out of its way to provide for them and instead be content with the bare minimum because the company behind that platform is evil because *checks notes* it's too popular and makes it hard for other corporations to act as middlemen and collect the game store tax themselves instead, i don't think you'll be able to convince too many people.