The reason for wood beds on trucks of old is still a reason there are wood floors in large commercial trucks and trailers, i.e. the BIG RIGS... ease of loading...
A wood floor does not bend, all else being equal, makind it easier, for a longer period, to enter and exit a vehicle with material handling equipment, like jacks and lift trucks... In addition a wood floor provided a means to secure the load... because you could literally "NAIL" the load in place... This method of securing a load is still in wide use today... Look at a flatbed trailer, for instance, and many times you'll see chocks or wood wedges nailed right to the floor... While still a need in the commercial world, the need died off in the "civilian" world, as it were.... Steel is easier to produce, easier to maintain, eventually the material costs became cheaper as well, thus easing the move over to steel floors....
Additionally, production wood floors, in small pickups and carryalls, were made of Southern Yellow Pine, not oak or maple, like we all install during rebuilds.... IT was real cheap, and REALLY durable, easy to nail to and able to take a real beating and still perform its job...in a day when trucks HAD TO WORK!!! not get groceries, or show off!!!
Pete
