Where did this idea come from that every device and computer must have the same interface?

That sounds like prima facie a bad idea. Actually thinking about it deeply only makes it fare worse.

I know! I want to fly a 747 with the interface of a Yugo. Sounds like a good idea to me.

Why would I ever want to use a 27-inch monitor with a phone interface? It amazes me what some people think is tranformative that is really just fucking stupid.