Wood decks were used on battleships even as late as 1945 for two main reasons. Firstly, it was highly useful for keeping the ships liveable. Wooden decking served to insulate the deck. Heat travels quickly through metal, and not so well through wood. As such, adding a wooden deck would help keep the ship warm in winter and cool in summer. As these ships were typically poorly ventilated and heated (especially in the Royal Navy), the decking was essential to keep the ships liveable. Having a wooden deck also helped reduce leaks through deck seams, which could form as the ship worked in a seaway. The other reason was that it made a good non-slip deck covering. Metal decks could easily become slick, especially when wet or oily. This could be mitigated through paint, but paint was just as heavy and flammable as wood. Many British carriers had steel decks, unlike American or Japanese carriers with wooden decks; American liaison officers with the British Pacific Fleet found that this resulted in a higher rate of accidental injury and aircraft damage than on American carriers. Wooden decks, however, were not without flaws. As you note, they were flammable, and required maintenance. Wood was comparatively expensive as a decking material, so many designs for smaller ships left it out, though this did require improved ventilation and insulation to be built into the design. Wooden decks could also be damaged more easily. The British Nelson-class battleships used fir, rather than the more common teak, as a weight-saving measure. Unfortunately, the light fir decking was found to be easily damaged by the blast of the ships' 16in guns, and was quickly replaced with teak.