This is a bit like complaining that you can't use an Xbox controller with a Playstation.
Apple Watch can't even be turned on without an iPhone. Have a look at PineTime - an open-source watch that can work with anything you want, or by itself.
How can you say that? I can’t run home brew games on an Xbox due to intentional locking down of the device by Microsoft forcing me to buy games they bless to be on their platform.
But some how these companies get a pass but Apple gets constantly blasted for this practice?
For the record, you should be able to do these things. But that is somewhat of a naive view of the world.