dash bar question

Why would one not put in a structural significant bar under the dash if they are going to add a cage in the first place??? If one wants to upgrade later to go faster down the rosd. Perhaps it being there already will savr them the hassle and cost to do it now.
I have one in my car, I am just stating that it is not required so if he chooses not to put one in he will be just fine, I have built plenty of cars without them, the car's cert to 8.5 and the owner is happy