I know that trends, researches, and studies often mean nothing. So there's probably more of the same shown here. Some of the data does makes sense though when used in a calendar setting, when looking back in the past.
The tags used above were programming languages that I have run into in the last 20 or so years. Languages like Pearl, I consider to be as dead as COBOL, FORTRAN, and BASIC. Ruby is headed in that direction. Objective-C is obviously on the downward trend because it had been canceled after Swift's introduction. Go is still going along. I forgot to add Rust to the tags, which would be crawling behind Go.
Above, we have GUIs being charted. Technically, they are decorated widgets for our OS's default GUIs. I started with X Windows, and obviously Mac before that. But the NeXTs and SPARCs got me interested in designing by own GUI for Microware's OS-9 Level II, which ran on the TANDY Color Computer 3.
Gtk was an ugly version of that GUI I made when I first saw it in Python's built-in library as tkinter, which is only becoming popular because Python is becoming popular. I've tried wxwidgets, and have made videos about how clunky it is. Kivy looks like a modern/contemporary GUI. What you see used on most hand-helds these days.
Qt (pronounced as either "q t" or "cute" still) had a great start coming out of the gate because of its professional design and clean look. And it has remained the easiest GUI to write programs for.
