If you add a billion users to Youtube or to Facebook or to any other major platform, the marginal costs won't be 0 or close to 0. They'll be substantial. Exist

If you add a billion users to Youtube or to Facebook or to any other major platform, the marginal costs won't be 0 or close to 0. They'll be substantial. Existing servers won't account for the new demand. Electricity needs to be generated, new hardware needs to be procured, more employees need to be hired, etc. So I'm having trouble understanding how we're entering an age where the digital entities have marginal costs approaching 0. For a single additional customer, that's true - their costs are effectively zero. But if you start adding millions of users, the costs are not approaching zero.