Slice of Life is defined by its lack of a conflict, plot, or storyline. It's all about having those cute or funny interactions between characters and their environment so that viewers can escape into a relaxed, casual version of reality. At most, slice of life can serve as glorified advertisements for various activities like camping or cooking.
Most American shows serve to provide excitement, drama, and conflict for the bored. Even the light-hearted comedy shows can have a pinch of cynicism or politics sprinkled in. The two closest things I can point to for American equivalents are KOTH and Seinfeld.

You are confusing slice of life with iyashikei, they are not mutually the same. While slice of life IS most about mundane life, it's not necessary only lighthearted comedy. Clannad, everything from Inio Asano, Mushishi, 3-gatsu no Lion and Otouto no Otto are some examples of defnitely-not-comedy SoL that comes to my mind.

Iyashikei however are a sub-gen of sorts of SoL, they are mostly works made to to "heal" the audience, but they aren't all necessary comedy either, Natsume Yuujinshou is a iyashikei that's not focused on comedy.

PSA: If you can, please check the works of Asano, he's one of my favorite author and makes some quite literally SoL works. Subarashii Sekai and Punpun are easy one of the favorite mangas I've ever heard.