The point is, they can't have a fire extinguisher until the engine damage is remodeled. That way they can put the fire out but they lose the engine. For now, if HTC put extinguishers in bombers in 2.05 patch 2, there'd be no point in shooting bombers. The best way to kill a bomber is to set it on fire, but if the fire gets put out and the bomber has no residual damage, what's the point?
However, if the fire gets put out but the bomber loses an engine, it is more vulnerable (but won't fall apart when the fire burns out).
See what I mean? Putting it in now would make bombers super invulnerable.