The short answer is that we absolutely need more trees than we currently have, but trees alone won't be able to get us there.

Trees are great at capturing CO2 from the sky, but they suffer from an impermanence issue. Trees capture CO2 for the duration of their lifespan, but when they die, they decompose and release that captured CO2 back into the atmosphere. They also require dedicated use of large swaths of land to get to significant capture amounts.

More info can be found at section 3.2 of this report: https://iopscience.iop.org/article/10.1088/1748-9326/aabf9f

Even better, faster and more efficient than planting trees is increasing organic content of the soil. The soil has higher agricultural quality, can hold much more water and the capture is long-term, as long as the soil quality is kept. And you do not need new acreage, you imrove existing. The problem is: you have to stop using fungicides and herbicides and better pesticides too. At the state of the current ag, this can be done for many many yeas.

Planting trees is great but long-term it won't be enough, just based on land area available. We need to scale up other ways to sequester carbon too.

Keep in mind that planting trees != planting trees. It's much more important to let natural vegetation grow on land than to plant random trees. For that, the most important thing we need to do is to reclaim land. Currently, 45% of land is used for livestock agriculture. You see what I'm getting at :-)

This is exactly my question as well. There's no way it's cheaper than planting trees and is probably orders of magnitude less efficient. And the plants itself must be producing an enormous amount of waste of pollution itself.

I would guess because you can actually make money with this capture technique and reduce emissions - planting a tree for the sake of reducing emissions is nice but it doesn’t make money and therefor isn’t a market based solution