I always wonder with runes if there is a huge survivorship bias. Runes most likely lack horizontal strokes to be easier to carve into wood, but wood doesn't endure time as much. Also with stones there's probably a similar effect: in central Europe stones like sandstone or limestone are more common. They are weathering faster than other stones.
Wood can endure surprisingly well depending on the environment. E.g. we still know that https://en.wikipedia.org/wiki/Onfim is a wild beast 750 years later, even though it was written on birch bark.
It's well known in protohistory that most of the religious sites were wooded, both with idols and altars of wood, but also in the forest itself in special places such as groves. The romans destroyed most of it, and later the christians (but I repeat myself). So I think gp is just reiterating this.
Here in America our high country and high country desert really make us lucky for having close to surface access of ancient things, makes archaeology and paleontology much easier.
I'm saying that maybe writing runes on stones was uncommon compared to write them on wood and that maybe runes were more common in central Europe than what we see, because those runes endured less than the ones on stones in Scandinavia.
If it helps any, the earliest dated rune is from a bone comb, and have also been found on wood and wax. https://en.wikipedia.org/wiki/Bryggen_inscriptions says that find helped show that runes were used for things besides "inscriptions of names and solemn phrases."
This would suggest that were runes widely used in central Europe, on wood, then it would still be possible to find traces of that use.
FWIW, knowing basically nothing on the topic, I did a Google Scholar search with 'rune "central Europe"', which returned things like:
