SteamOS is better than, for example, macOS and Windows because of licenses.

Since you're new (welcome!), I should let you in on a little secret: pretty much the entire free software movement is built around licensing. I know, it's boring and seems insignificant. But the outcomes are profound.

Because SteamOS is built to function within the free software ecosystem, it means users are never beholden to the decisions of one centralized entity (usually the company that owns the software patents.)

If Valve ever decides to, say, include candy crush ads in SteamOS' start menu (they'd have to make their own start menu, since right now SteamOS uses one that's already made by the free software community), then users can choose to remove that part of the menu or replace the menu altogether without having to start from scratch.

For wealthy people who can always pay the "proprietary tax," this might seem like a non-issue. Practically speaking, these people only want their software to work without hassle. They don't care about the true cost of that software, such as only one entity being able to modify/distribute the software. It's not until, say, photoshop starts charging a subscription (which they can always increase the price of) that people start to see the value in free software and the importance of licensing.