Yes, absolutely. Approximately nobody translates technical documentation for fun, much less at such a high level. The article is pretty clear that the number of languages supported is a business decision.
> Hell, who would write hundreds of thousands of wiki articles about The Elder Scrolls universe for fun? https://en.uesp.net/wiki/Main_Page
70k articles, not hundreds of thousands,[1] and of those 70k fewer than 1/3 are translated to any other language.
And speaking as someone who was a system and content admin for a MediaWiki-powered fiction wiki of about 15k articles... there are not many people relative to the amount of content who are actually interested in contributing anything, much less improving or maintaining what's already there. It's a very, very small core of contributors.
Toward your example, the 161 "active" users[2] (meaning any number of edits in the last 30 days) as of today on English UESP combined for 5,974 edits in that span. Of those edits, 4,779 were from 13 users. 3,039 — more than half of the last month's activity — were from the top 5 users.
On the non-English UESPs? No active users in Portuguese, one in Italian, none in Arabic.[3][4][5]
From my experience at least, it's because it's work — fun work, at times, but still work. Translating MDN content is also work. Doing _any_ documentation of _anything_ is work. Hell, I burned out on fiction documentation work before I burned out on paid work.
Some people do enjoy it! But voluntary documentation is still going to attract a small, specific core group of consistent contributors (if it attracts any at all).
Your comment is the same as people who saw the launch of Wikipedia and wondered who could possibly write articles and find citations for fun.
Hell, who would write hundreds of thousands of wiki articles about The Elder Scrolls universe for fun? https://en.uesp.net/wiki/Main_Page