It doesn't just matter, it's can be huge depending on how you plan to use your oven.
Baking pizza is a matter of top-bottom heat balance. Without proper heat balance you end up with a pie that's burnt on the bottom and white on top or vice versa. Below the pizza, the heat is a function of the temperature and conductivity of the baking surface. Above the pizza, it's a matter of IR radiation from the dome and walls of the oven, the temperature and conductivity of the air, and convection.
The conductivity of the baking surface in a wood fired oven can vary quite a bit with something like biscotto di sorrento or saputo which are probably down near 0.3W/mK to certain fire bricks which are 1.3W/mK. By comparison, a typical cordierite pizza stone is about 3.0W/mK and a steel plate which is about 50W/mK. To make it more confusing, the conductivity varies (increases) with the temperature and not everyone measures conductivity at the same temp.
For a wood fired oven that is going to be used at very high temperature - such as for Neapolitan pizza - you need very low conductivity. The floor material supplied with most WFOs is too conductive - some are way too conductive - for Neapolitan pizza. In an oven like this, you end up needing to "dome" the pizza which means lifting it off the deck with the peel for a portion of the bake. Depending on the oven, it might be half the bake.
There are probably several reasons why manufacturers use higher conductivity decks including the fact that many simply don't know what they are doing. However, for the most part they are probably building middle-of-the road oven knowing that most people will never try to run them >850F. At lower temps, a bit higher conductivity works better.