Also, I suspect the actual answer is that knitting patterns as a general concept aren't actually all that interesting, what people are interested in talking about is the things you can do with them. So there are a lot of fairly old, long articles about various knitting stitches and techniques, traditional designs, yarns, communities etc but no-one created the "knitting pattern" article until 2015. The otherwise extremely long and detailed article on knitting referenced patterns even before then, there was quite a bit of information about where to get them, and the various row counters used to keep track of where you were within a pattern had a huge article covering different types and their history, but nowhere explained what a pattern was and how it worked!
(The other interesting thing is that a lot of the knitting-related articles were obviously created by women, as you might expect, but the article on knitting patterns was created by some guy as his first edit. His only other edits were an attempt to split up the content in the extremely long main knitting article into other articles which was immediately reverted. This probably does show something about some kind of flaws in the Wikipedia model, but probably not the ones you're assuming it does.)
These attempts are inherently hard to arrange, often requiring a long discussion on some agreed-upon Talk: page. Wikipedia does not have an equivalent to the git sites' "merge request" workflow where a set of diffs to multiple pages can be worked-on in "draft" status and then transparently merged; these things have to be arranged manually.