Apple went all in on Java, but the developers didn't follow. The unusual syntax of Objective-C was always seen as a hinderance to OpenStep/Cocoa adoption, and

Apple went all in on Java, but the developers didn't follow. The unusual syntax of Objective-C was always seen as a hinderance to OpenStep/Cocoa adoption, and Java was seen as the solution to that problem. But Java wasn't a perfect fit for AppKit development, and once developers wrapped their heads around Objective-C most of them stuck with it rather than deal with Java/Cocoa idiosyncrasies. With few developers, the Java/Cocoa bridge died.