That would mean exclusives everywhere. Everyone would try to force some game pass on us, until our only choice to get an OK selection would be having 4 subscriptions. Or piracy.

With Steam, I get a well integrated platform for buying, updating and launching everything with the correct compatibility layer.

That's more convenient than piracy, so I use it.

"Not being a total bastard" is a weird way to describe overhauling the gaming on linux experience at no additional cost to the end user, among many other incredibly pro consumer choices they've pushed in the last twenty odd years.

Honestly 20 different companies would probably suck for the consumer. That's 20 different storefronts to compare, 20 different libraries to manage, potentially 20 different sets of logins, 20 sources of data breaches. It's unlikely they would adopt an open standard to allow a shared library. Maybe you have a 21st company that makes a product like heroic launcher. You'd likely run into regionality issues where a particular store is unavailable, so you may not be able to play purchased games. You would have all sorts of odd exclusive dlc and pre order bonuses so a cosmetic item you like could be locked to a store you haven't used. Multiplayer likely wouldn't be global cross play between all companies, you likely get some set of 20 companies working together for multiplayer. Some games may develop a good scene available to a single store, requiring a game to be repurchased. Exclusives or timed exclusives would be annoying to track, as each store would likely have different catalogs.

I simply do not understand the sentiment that not being a total bastard is something celebrated and not expected or required.

It’s simple really. If you don’t give positive feedback, you’ve lost the major lever that can be used to get what you want.

Using negative feedback is a useful tool but it’ll never achieve the same outcomes if used by itself.

And while many like our Steam benevolent (almost) monopoly, I do wonder how would the market look like if we had 20 competing companies that cannot gain more than 5% of the market share. Can you imagine the competition between them and how would that benefit us, the consumer?

More comptetion wouldn't just benefit consumers, it would benefit devs. A dev could shop their game around go with a store front that suits their needs better.