so americans keep their shoes on when indoors and

Yes...I'm sure not every American household does, but that was one of things I had to get used to when I got married (my wife is from Ukraine). I used to just wear my shoes everywhere all over the house. "The Middle" did a great job (IMO) of portraying life in the midwestern U.S. That part rings pretty true, IMO.

only in the midwest

Shoes come off when you come into our home.

Nobody I know does that. We wear slippers or rubber flip-flops inside the house.

It is a gross habit but many do.

Taking your shoes is is considered getting comfortable. I take them off in my own house, but I’m in a strangers house, or someone that I don’t know that well, I’m not getting that comfortable.