Because it is not as easy to just export to the Switch format and be done with it. You have to sign up for a Developer account and get your project APPROVED by Nintendo.
You have to meet all of Nintendo's TRCs (technical requirements checklist, joycons, 720p mobile & tabletop, 1080p dock switching, wifi and wired ethernet, etc), you have to make sure the content of your game matches for the ESRB/PEGI rating you are going for, Nintendo has their own rules and documentation that you have to carefully read and follow if you want to publish and stay on the eShop.
I have heard the Nintendo dev kits are around $600 depending on fluctuations and other variables like support for the 4k kits. Nintendo does NOT require you to be a LLC or Inc though. Playstation/Sony does, their dev kits are way higher (if you have a great demo and contact them they have given them to indie devs for free before).
