Why do americans pronounce "our" as "are"?

It’s just the way we speak.

We don't, we say hour.

nice way to paint americans with a broad brush.

Not true.   Everyone I know says "our."

Why do they pronounce it as "r" more like.

I've heard that in utah.

Probably just a slang term, like how British call each other mate.

They can be forgiven as they have an American accent but it is in writing, are and our, it is an English major's horror story.

Americans who speak correctly do not do that. Some people just have sloppy speech habits.

some may have an accent that make it difficult to differentiate the two.  but most understand grammar to say it properly.