Those are only the "notable" languages. If we consider less than notable languages as well, we might get something like the languages on Rosetta Code [1]. Looking throught the history of that page, I see that about 10% of the current 834 languages were added in just the last 5 years. Which is much less suggestive of a downward trend.
[1] https://rosettacode.org/wiki/Rosetta_Code/Rank_languages_by_...
https://en.wikipedia.org/wiki/Timeline_of_programming_langua...