> Have we really not understood OO at all so that we have to reinvent it all the time?

We haven't. I think the popular OO languages shows this. In both Java and .Net the focus is on classes, not on messages passed between objects. But class hierarchies are not essential for message passing. Classes are mainly a way of decomposing an application into manageable logical parts of interacting chunks. Looking at how many language features center around classes and class hierarchies (interfaces, abstract classes, generics, inheritance etc) as opposed to how many facilitates different forms of interactions between objects (you basically have method calls and arguably async/await) it seems clear to me that these languages are more "class oriented" than object oriented...