Re: Target market?
I suspect the target market is largely people who like PC games, like using steam, but are hitting the point where they can't afford to keep a "gaming" PC going with the average mid range video card now being £300-400 or more on it's own.
I suspect "hardcore" PC gamers are an increasing minority of steam users as steam has been so ubiquitous with PC gaming for so many years that people install it to play pretty much anything and will install it on all sorts of hardware as even on a low end laptop there are games on steam (often good ones) that will play.
I know a few people who would love to get one for their kids to game on, and several very long time PC gamers who are really annoyed with graphics card prices and would jump at the chance to get a whole system that can play most/all the games in their library for less than it's going to cost them to replace their video card,
The thing to remember is that most PC games, even new ones will run on hardware that is ~3-5 years old, I was running quite happily on a PC that was nearly 10 years old for the CPU and 3+ years old on the GPU until I upgraded it completely couple of years back (I had plenty of ram and a couple of SSD's which helped a lot).
Steam is great for that sort of thing, you're not locked out of games that are 5 years old because they've not been ported to the PS5 from the PS3, and a lot of games released on steam are smaller less ambitious ones, but great fun and will run on very low spec hardware.
As I believe has been said before, Steam know exactly what hardware people are playing on, and they know the games they're playing on that hardware, from a quick look at Steam's hardware survey results I always tend to notice the "hardcore" PC gamer with the top end video/cpu/ram tends to be a very small percentage of the total users (I'm always amused that I tend to be in the top range for memory as I put that as a higher priority at build than GPU - 32gb 12 years ago, 64gb two years ago).