[PeterisP]

It's difficult to get enough total quantity, and it's also not rapid enough as it takes decades after planting (which would also take a lot of time) to soak up that extra carbon.

One aspect is that the required land area - https://climate.nasa.gov/news/2927/examining-the-viability-o... mentions 900 million hectares (2.2 billion acres), which would roughly cover the 10Gt/year asked by the x-prize - is enormous, and it's not an accident or negligence that this land isn't forested now, it's generally because we turned it into farmland or pastures.

Are we willing to take away 900 million hectares of land that produces food for the world and money for the locals away from that productive use and turn all of it into unproductive forest that won't get used for logging? Perhaps we are, but if there are other options for carbon removal that don't require as much land resources, that would be preferable.