That's true for a lot of people, but I truly believe a very significant number of people are being exposed to Linux this way and will stick with it long-term. It will be a while until we see that reflected in the desktop and laptop statistics.
I haven't used SteamOS (or even seen many videos of it), but from what I've heard it's not shy about being a desktop operating system. Even the Steam Deck, which is marketed as a console like you said, lets you use it in desktop mode and run any Linux software without having to jump through any hoops. This isn't like Android which is technically Linux deep under the hood but effectively completely detached from the Linux ecosystem. SteamOS is part of the Linux desktop ecosystem, and it's proud of it.
I think smartphones definitely win when it comes to convenience, accessibility, and ease of use. Even at home I use my phone a whole dang lot for general chill purposes, even though I have bigger and better screens to use.
I can't comment on porn because I genuinely never watch porn of any sort (yes, I'm serious), but I have watched and enjoyed YouTube and Netflix et al on my phone, even at home. I usually prefer a bigger screen but sometimes the portability wins out.