The switch has sold 100 million units now, that’s a big and diverse demographic. There are a sizeable chunk of people with a switch who weren’t even born when Portal 1 came out, have no PC that they game on, let alone a Steam account on which to buy it. That’s not even considering that people who may have a PC but prefer to play on the TV or handheld, cos that’s a better experience or where their friends are.
It could have been priced higher and would have sold well. $20 is a good price for both games. That it’s even comparable to the current PC price for games that have been available on that platform for over ten years is notable. I get it’s not an attractive proposition for you, but it is for a lot of other people.