I wouldn’t name it a mistake, that’s too hard. I fully understand that the doc site was migrated to GitHub pages. Unfortunately, this was made without any design and styling. And this is the point where changes should apply, urgent and comprehensive.
There is no communication by the developer. It is not common knowledge that the site was migrated to GitHub pages and to be honest, it should have been mentioned before happening.
Even many versions ago when the docs were part of the installation and selfhosted, it got changed and just done through a changelog. Its wrong.
Such popular software is no point being open source if the community is restricted and not even communicated to properly.
Of course, you’re fully right, but … 
but…? what have I missed? 
There’s nothing coming to my mind.