Ask HN: Why is it so hard to design an open-source smartphone?

Following the discussion around Librephone [1], it seems that every project regarding open source smartphones OS are centered around the software only.

Lineage and GrapheneOS have proven that reverse engineering is hard. So I'm wondering why can't we have a project that starts from scratch and build the electronics and the OS? In the same spirit of what Apple did with iPhone+iOS. I'm sorry if I sound naive, I just don't realize how hard it is to design a smartphone.

[1] https://news.ycombinator.com/item?id=45586339