There are industries that use the same raw materials, yet are not the same. Commercial firms that deliver purified water to companies consume water, fuel, and vehicles. Yet, not a single one is in competition with the local swimming pool company.
Guys trucking 5-gallon water jugs around to offices are doing something with the same materials that is completely different than what the other company — digging, lining, and purifying your swimming pool — is doing.
So, are open access publishers and traditional publishers really in the same business?