I also don't understand this question. The default launcher is like twm on Linux. It's only goal is to give you some initial GUI so that you could install something you actually like.
Your question doesn't make sense, GrapheneOS said that they prefer spending their time implementing and fixing security issues rather than things that can be easily changed from open source offerings. See https://news.ycombinator.com/item?id=47247778.
I am aware that the keyboard can be changed.
The question is why I have to change them, when the Lineage versions are open source?