It must confuse English learners to hear phrases like, "I'm home", instead of "I am at home." We don't say I'm school, or I'm post office.

Because home isn't a normal location, it's "home".

It's where you're from.

Like, no one says "I'm house" or "I'm apartment building" because it's not about the physical structure. It's about being where the heart is. How many pillows do Grandmas need to stitch that on?