As Please Stop Citing TIOBE (https://nindalf.com/posts/stop-citing-tiobe/) points out, languages do have random fluctuations. It’s garbage data, so this is unsurprising. Between 2016-17 Java dropped 42% and C dropped 62%. That indicated nothing then, because they both promptly recovered. It was just noise.

Don’t take TIOBE seriously. You’ll feel better.

Look at the other suggested metrics - Google trends, GitHub repos, Developer surveys etc. None of these are perfect, but they’re more meaningful than TIOBE.

Well ruby has been in decline for the past 10 years... https://trends.google.com/trends/explore?date=2016-12-02%202...

and it's not even worthy of being compared to python, the line is so insignificant that it looks flat https://trends.google.com/trends/explore?date=2016-12-02%202...