I'm just guessing here, but I don't think that Apple is all that interested in making it easier to develop cross-platform applications. From their point of view, the best applications are OS-specific ones. So if you want a Mac application, you're best coding on a Mac, with Mac tools, and within that hardware eco-system. From this point of view, the same argument applies with Windows, Linux, etc... (albeit with the caveat that hardware is more varied).
Apple isn't trying to make that way of working easier... they are trying to make life easier for macOS-specific devs. Apple is looking for well integrated applications, and as I'm sure you know, that's really hard to do well cross-platform as you often end up coding to the lowest-common interface.
Apples interest in making cross platform applications easier waxes and wanes with their market share. If I remember correctly, they were quite keen on java and making it work well at one point.
They still heavily use Java on their backend systems, but that's not what we're talking about here...
You're right - they did have a Java-Cocoa bridge early in OS X, but deprecated it quickly when it was difficult to translate Obj-C semantics into Java. I remember trying it, but it wasn't really that easy to use. Even in this case though, the idea was to write Mac-specific applications, just in a different language. Most of the application's magic was still in the ObjC/Cocoa layers, which weren't cross-platform (or were they - I can't remember if there was a Windows port at sometime??).
While this would have made it easier to write cross-platform applications, realistically, that was never the goal. I think the goal of the Java-Cocoa bridge was to offer a backup plan in case too many devs didn't like Obj-C. At the time, Objective C was a novel language for many people. Once Obj-C got enough mindshare and it looked like it got enough of a buy-in from developers, Apple ditched Java quickly. I'm sure the licensing issues from Sun in the early 2000's didn't help matters here.
Also, it's only been fairly recently that Apple turned over the Mac Java port back over to Oracle. For the longest time, Java developers on Macs were always a version or two behind because they were on the OS X release schedule, rather than the Oracle/Sun release schedule.
The Java-Cocoa bridge was only an early bet as they weren't sure if the Mac developers were keen in jumping into Objective-C.
They dropped it the moment they realized most of them were happy to use Objective-C and somehow they were the first company to turn back the tide from JIT to AOT compilation.
Yes, back in the NeXT days there was a Windows version of the whole Objective-C dev environment for Windows, and also an initial port of Cocoa to Windows when it was still called Rhapsody.
As for fairly recent, it was almost 10 years ago. :)
Not only Apple, that was the culture in the 80 and 90's home computers, as you mention.
Which again is hardly different from UNIX culture, which doesn't matter what the hardware is capable of, as long as, it runs UNIX and given that the UNIX culture never cared for the desktop experience (Xlib and Motif really?!) that gives a clash of cultures.
Apple isn't trying to make that way of working easier... they are trying to make life easier for macOS-specific devs. Apple is looking for well integrated applications, and as I'm sure you know, that's really hard to do well cross-platform as you often end up coding to the lowest-common interface.
Again, that's from the Apple point of view...