Well most IOT tech is simple if you break it down into basic IT terms like you have, but someone still has to develop the hardware specifics and do the dev work to build the app/front end and customise it and make it smart, feature rich, useful and easy to use...then manufacture as a nice looking product. Ohh yeah then you have to market it and sell it - hardest part!
Yes you could probably mock up a half a** version with a raspberry and some other very basic open source or other basic front end but it's still going to be "basic" and not look pretty. I am sure China have one in the works..lol
It just aint as simple as you say otherwise everyone would be doing it!