It's literally based on the (estimated) number of search engine hits for e.g. "Python programming" on Google and a handful of site-specific search engines (e.g. Amazon, eBay, Walmart, microsoft.com, etc), with some manually applied tweaks for languages with easily confusable names. Many of the fluctuations in rankings - like the big dip in the ranking for C between 2015 and 2018 - probably have more to do with changes in search engine algorithms than any real change in popularity.
It wouldn't surprise me if I learned that the vast majority of programming globally is in languages like Visual Basic or PHP that are utterly unfashionable on a board like this, but still make the world go round.
It's a bit hard to comprehend that's reality to be honest.
But I could see that it could be the case from the fact that old industrial factories or old corporates would still run with what works for them.
Because TIOBE's methodology is terrible, and always has been.
https://www.tiobe.com/tiobe-index/programminglanguages_defin...
It's literally based on the (estimated) number of search engine hits for e.g. "Python programming" on Google and a handful of site-specific search engines (e.g. Amazon, eBay, Walmart, microsoft.com, etc), with some manually applied tweaks for languages with easily confusable names. Many of the fluctuations in rankings - like the big dip in the ranking for C between 2015 and 2018 - probably have more to do with changes in search engine algorithms than any real change in popularity.