alt Hacker NewsSimple language isn't just for children. It's also good for non-native speakers. Besides, even for those who can understand complex grammar and obscure words, parsing unnecessarily complex language takes extra effort.
In this specific case, I don't think the rewritten version of the document is infantilizing.
It's not useless, but the original document is aimed at expert craftspeople and there's a lot of content in the texture of it.