wood has a limited life span. It can be damaged, rots, soaks with water... and gives splinters! the steel deck is much more robust. My last trailer was 15+ years old & steel deck and I didn't have to replace the wood deck once and was seemingly indestructible. but also non auto items are easier to slide around, move, position, blah blah blah. also, I haven't seen a wood one with a dovetail longer than 2', usually they are really short. steel decks can often be found with 4' tails, makes loading really nice.
... I just want a steel deck one. but maybe if a really good but cheap wood one comes along I'd consider it.