I don't think it's quite that simple. I'm not in the business, but every time this comes up someone points out that stores don't actually always buy inventory. Often times they are simply selling the shelf space and it's up to distributors to stock it themselves.

It's still different. For those retailers (e.g. Best Buy is a good example) they're leasing floor space in what is essentially a public warehouse.

You still need to outbid existing inventory space, which is not the same as an open platform for anyone to sell through.

yep. Online platforms can just peek at the data and when they see something selling they can make their own version. They are taking zero risk.

In contrast brick and mortar has no idea what does well until they start buying the product to sell themselves.

I know a rep who leases freezer space from our local big chain grocery store and is responsible for that area. Ive heard of quality issues from this specific ice cream before, and it always reminded me of getting poor quality items from non-amazon sellers.