This land is not already being used for forests because other uses are simply more useful or less costly. The net loss of utility then needs to continue for as long as the carbon is sequestered.
Finally, if you want to sequester carbon somewhere else you need to collect and transport it which adds more costs. Further, if that’s the goal forests are simply slow carbon sinks in comparison to other plants.
You're correct, nothing comes for free, but the alternative is to leave this dead standing wood on forest floors to be later fuel wild fires. Or in the case of agricultural waste, to be composted or burned directly. Seems like a waste, as composting produces methane and CO2, which unless captured in an anaerobic digester just goes into the atmosphere and contributes to global warming, and burning does similar harm.
Small scale gasification reactors can run equipment, and are easily transported on trailers to the site of waste if it is not already easily centralized (in which case a dedicated cogeneration plant is usually a better option). A 20kW reactor can produce enough electricity to run 16 US homes, so situating one on every block is also a viable option that we should be considering.
Not sure how any of that is expensive, as it fulfills our requirements for food, housing, and luxury goods.