You are wisely thinking "but wood is flammable". True, but the idea is to block the area off so roof ventilation from the other units does not "draw" the fire. Think about it, roof ventilation, to a fire, is like a chimney. The party wall at this new condo is at the right side of the photo. In older units, 20 or so years back, access to one attic hatch often lets a person in above every single unit. In fact, if there is more than one hatch, that can allow someone in the attic easy access down into places he or she should not be. That can actually be a security and privacy concern. Hollywood has played that one up more than once in movies.
Steven L. Smith
Bellingham WA Home Inspections