* There is usually no clear way for a UX designer to contribute. Note with this example, under 'Contributing - Tasks I could work on' it doesn't mention UX, and the only way to become a committer is to "show us some of your patches, or solve some issues" - none of which involve UX.
* There is a slight obsession in the open source community to use only using open source tools, while the majority of modern UX practice is developed on proprietary tools (e.g. Figma).
* Design by committee is the most frustrating and slow process, and great UX design comes from strong decisions by great designers rather than community votes.
* There is an underlying assumption that if you contribute UX designs and put them in the Wiki they will be ignored, so there is no point. It's not the same as code where there is a one step process (i.e. commit), the whole team needs to embrace the UX and then work to commit it to code.