Why can wood burn all the way to charcoal instead of just creating a passivating charcoal layer?
Charcoal doesn't passivate and the results you see depend on the physical structure of the fire

The difference between a match and a larger wood fire has little to do with the formation of charcoal and more to do with the circumstances of the reaction. And the charcoal isn't really passivating in the reaction on a match.

Wood consists of a complex mix of chemicals as well as the core cellulose, which is a carbohydrate. Some of the ingredients, like the sap and other volatile components, burn easily. Cellulose burns in multiple steps one of which involves pyrolysis where some components are driven off quickly leaving mostly charcoal. Charcoal itself will burn but it takes more energy to ignite and therefore more time to get going. It isn't so much that charcoal passivates, it is just that it is the last component to burn.

The difference between a match and a larger wood fire isn't about passivation but about the scale of the fire. There isn't enough energy in a match head to drive combustion all the way so only the easy-to-burn components ignite (unless you hold the match upside down so the flame spreads up the matchstick when the heat from the tip is enough to cause much more extensive combustion). In a larger wood fire there is enough energy in the flame to cause more complete combustion. So the volatile components burn quickly but leave enough heat for the charcoal to burn as well. Since heat penetrates charcoal very well, the volatile components under the charcoal will tend to ignite before the charcoal itself (it isn't doing much to passivate the wood underneath). In a badly organised fire the overall heat may never be enough to set off the charcoal.

So the issue isn't passivation just a reflection of the order the components of wood burn and the physical structure of the fire. Charcoal isn't passivating, just the last component to burn and, if the fire isn't well constructed, there may never be enough heat to burn it. Much more of a match will burn if you drive the flame along the stalk by holding it upside down and a well organised fire will burn the whole way to ash.

Also controlled pyrolysis (which is used to create charcoal deliberately) relies on controlling the amount of air available to the work being pyrolysed. If there were enough air, the charcoal would burn but the conditions for pyrolysis involve restricting the air so the end-product cannot burn. Charcoal doesn't passivate anything when there is enough air (which is why you can cook on a barbecue).