Would it be possible to not pay the full price if you already have paid the PC version ?
Nintendo didn't make any money from the PC sales, so it needs to have revenue from this launch.
And for Factorio itself, the effort of porting to the Switch, and then the effort of going through validation with Nintendo. Even if they didn't want to charge you again, the company would need to cover the cost of dev kits, extra engineers, and a whole extra channel for development/release.
I don't care. Factorio devs can have my money.
And because they demand active involvement, they save you from spending money on other stuff. You can easily shop online on the couch watching TV. Not so much if you're playing a game or a sport.
There is a dark side however, in that gamers can sometimes completely lose interest in the act of gaming in and of itself. This is a complex range of emotions related to the sensation of aging and the restrictions that come with responsibilities. But when it comes, it can alter the value of what people get from games to devastating effect.