We now have GPUs, mobile OSs with their own separate UI abstractions, the web, WebAssembly, etc. And people want write-once deploy anywhere.
You didn’t have any of that 30 years ago.
Now you can just choose 1 compiler such as GCC and it works the same on all platforms; even cross-compiling to a different CPU architecture works well and is far easier to setup (before it was a black art).
"Ubiquitous Applications: Embedded Systems to Mainframe"
"To support a variety of platforms, Smalltalk uses a virtual machine approach to portability that allows applications to be easily migrated between platforms with little or no change to the code."
https://dl.acm.org/doi/pdf/10.1145/226239.226264
~
"… Smalltalk developers can work and deploy on Linux, Windows, AIX®, Sun Solaris, HP-UX, and OS/2®. You can also create applications to be deployed on the mainframe with VisualAge Smalltalk Server for OS/390 and z/OS."
https://www.ibm.com/docs/en/announcements/archive/ENUS202-10...
Java ?
My point was that making GUIs today should not be any easier than 30 years ago because we have a lot more complexity across different OSs, phones, and the web.
Update: I think I understand your comment. I think you latched on the very last past of my comment about "write-once deploy anywhere". I meant that as in people want to create their GUIs with one language and one toolkit and have them deployable across different stacks without having a custom version for each and every final target platform.
Yes, technically Java did deliver on that as a programming language and runtime. And I guess swing also deliver on that as a cross-platform UI toolkit. However, we don't see a lot of Java UI applications around, with the exception of a few big ones, so it's fair to say that in the end it didn't work out. Of course, Java as general purpose language and runtime is alive and doing well today.