Nintendo has fans and is an established brand. But I think what most people dislike is the uncertainty. With the Switch you can know for certain all games you buy will work, but with the Steam Deck it’s not guaranteed though it will scan your library and give you a rating. Though in my case I had many “unsupported” games actually work flawlessly.
The issue for me that had me buy a Windows 11 laptop was it was the cheapest I could find. Though I have since then given it away and replaced it with a Steam Deck as my only computer.