A lot of wikis leave the Help namespace empty because no one with sysop rights gets around to exporting the Help namespace from, e.g., MediaWiki.org and importing it to the local wiki. It's a multi-step process requiring several trips to Special:AllPages, Special:Export, and Special:Import on the two wikis since there are a few thousand help pages, for those who want everything. Maybe one will only want to get pages in [[mw:Category:Help]] and possibly [[mw:Category:Extension help]], though. See [[mw:Project:PD help/export]]
Another possibility might be for a wiki to get rid of its Help namespace and create a help: interwiki prefix pointing to MediaWiki.org, e.g. https://www.mediawiki.org/wiki/Help:$1 Then they give up the ability to create customized help pages, though.
Version: 1.23.0
Severity: enhancement