Because it isn't a problem with planting. That's very easy, and people volunteer to do it. When I was a kid (I'm Icelandic) we'd go on field trips and plant hundreds.
You sound like you doubt the viability of automated and distributed tree planting which may be more statistically significant? I get your point that hundreds may not do, what about hundreds of thousands, then?
Let's agree that we can't know as long as nobody tried. And you're right, we don't have the numbers on how the survivorship ratio in larger magnitudes would behave, it might just shrink to ridiculously small. But then again the soil would be slightly "improved" by a dead sapling, maybe even increasing the chances for another try?
> You sound like you doubt the viability of automated and distributed tree planting which may be more statistically significant? I get your point that hundreds may not do, what about hundreds of thousands, then?
No, my point was that if the solution is increased numbers, it's already cheap and viable to get humans to do it rather than deploying expensive tech.
(By hundreds, I meant hundreds for each group of 3 school kids in one afternoon.)
> Let's agree that we can't know as long as nobody tried.
I don't even know that nobody tried. I'm sure the actual experts (as opposed to us armchair ones) thought of it.
The problem is keeping the growth alive.