And yet they've decided to do it again, with yet another incompatible language! Joy of joys!
(And as for Java, it was my understanding that Apple had hobbled it by refusing to release updates on a timely basis.)
I can see how they could get tired of being forced to ship almost-monthly updates just to support an extra language with very limited adoption. If you have to make that sort of effort, you'll probably do it for your native tools only (like Microsoft does with .Net). Besides, Java apps on OSX looked better than Java apps on Windows, but they were still recognizably different from Obj-C ones.
I wish somebody would write an OS in Python 3...
That's a different, later issue.
Early on in the life of OS X, Apple offered a Java interface to the Cocoa class frameworks. In theory, you could write OS X applications using Java, calling into the Apple frameworks instead of using Swing or whatever Java frameworks.
This wasn't all that well supported, didn't perform well, and wasn't popular.