The Switch was weak when it came out. Decent PCs from that same year can handle most of these games just fine. It's not really the developer's fault when the Switch is the only platform with issues, and they're usually not "pushing the envelope" in any way. The fault here is Nintendo's, they didn't prioritize support for ported games, though admittedly they couldn't really foresee the indie game boom, since it wasn't nearly as big of a deal at the time, especially in Japan.

First-party Nintendo titles are more or less the only games that actually manage to "push the envelope" on the Switch, and that's because they have the resources and experience to do it. Even then, some games end up constrained compared to the original vision, because the hardware can't handle it no matter how much insider knowledge you have about how it works and how to use it right.

Most indie devs don't have time and money to optimize. They will make the game primarily for the biggest audience, and then make it somewhat playable for everyone else.

The closer Switch is to the Steam Deck, the more likely both will be targeted.

What a bizarre thing to say. People buy indie games for all sorts of different reasons, and sometimes it's the beautiful art style.