Well you might not, if your accessible market is 10 horses and 5 cars can fill that market need, then you're left with 5 people who aren't needed because your products don't meet the needs of 10 cars worth.

If your postal service services a population of a million people and it takes 1000 horses to do that easily, but it takes 500 cars, you don't have a need for those 500 extra people.

You can't deliver more packages if the packages aren't there to be delivered. Your product demand doesn't just magically scale up once supply meets it.