Then you could just use a metal plate or glass, but we use the wood in order to protect the blade of the knife also. You'd have to re-sharp the chef knifes every few minutes if they were used on the surface harder than the blade.
There's a foil edge on very sharp knives that will wrinkle and fold after use on anything, even tomatoes, making the knife feel dull. It's not, and it doesn't require removing metal as with grinding or sharpening, but you can steel to realign that edge or strop to hone it depending on the blade and angle. Even if you don't work with blades often, you've probably seen this depicted in media.
It really doesn't matter what the cutting surface is to the knife if you have great technique. Since I don't always, I use thin, flexible plastic barriers. I would never recommend wood outside of having no other choices or using it as part of presentation, mainly because of cross contamination and difficulty in sanitizing if you cook sous vide or serve raw often.
Obviously I meant the stone sharpening, not using the knife steel. And as for the material, many sources say that plastic actually contains more bacteria and that end-grain wood is more gentle to a blade than plastic. On the other hand plastic is easier to clean when it's new, but it's also more prone to cuts than wood and they quickly get dirty (at least in my limited experience). IMHO every board needs to be scraped or sanded from time to time to remove the top layer completely, that's the only way to keep it clean.
