Because then you have to transport the wood to the site, transport the ash (etc.) off the site, and build something useful to do with the produced energy. Most of that would be trucks or ships if it's on a navigable waterway.

Oil and pipeline companies are building pipes to move gases because it is the cheapest way to do it.

I think it's better to charcoal the wood and burry the charcoal. If charcoal is stored properly, it takes a lot of time to decompose and keep the carbon down there for a long time. And it has less storage problems than CO2 that is a gas and wants to escape.

Probably instead of wood, it would be better to use other agricultural waste. For example here, some sugar factories use the rests of the sugarcane ( https://en.wikipedia.org/wiki/Bagasse ) to burn it and produce heat and electricity. I'm not sure if it can be charcoaled and buried instead.