Basically win their hearts and trust early, so they can become loyal throughout their life.
So these devices had to check some boxes, one of the main factors being the price.
These devices had to be cheaper then regular consoles (among other things) - though they shared the same kind of price strategy between each other: sell almost as cost (or at loss in case of the PS3), to make up later with game sales.
Nintendo blurred that line into one device with the Switch, but they still check the box of the device being affordable.
With that said, there were already some approaches to Nintendo Switch like hardware for the PC market, some with waaaay better performance then the switch (with both intel or AMD socs), yet they are failing in what I believe is crucial for these devices: price.
They are expensive.
I'm not saying they aren't wonderful pieces of engineering, but clearly they aren't meant to even compete on the same level. They can't sell at cost/loss, because they can't make it up with licensing or their own IP, so they have to make money on the hardware itself.
Therefore I always assume these devices are for a very particular small set of gaming enthusiasts who are found of the idea of playing PC games on the go (even with limited battery life), and are willing to pay more then a full fledged console for this experience.
I'm curious to see how Valve will tackle this, or if they are fine with that (which they seemed to be in other hardware releases).