Grapheneos is, to my understanding, a dedicated development effort that specifically targets pixels.
Lineageos on the otherhand, provides scaffolding that volunteers can use to support phones of their choosing. It's very best effort and ymmv between phones. A universal upgrade option is just asking for trouble as it's not guaranteed all phones will behave the same/well.
That'd end up being a longish explanation of what wlroots is, and I think that'd detract from the post. Noting the vacuum exists and linking to the emergent library that filled is sufficient, and gives the curious reader something they can follow up on.
For discoverability. Someone's trivial finding may be someone else's key to a major breakthrough, but little good it does if it can't be easily found