[modernpacifist]

Not exactly - they apply to whichever dictates your capacity - be it ingress or egress. Overwhelmingly, capacity for hyperscalers is dictated by egress peaks. Since most non-residential network links are delivered symmetrically, the capacity for the other direction is already there as a by-product.

Also don't underestimate the benefit of simplification - why bill for 2 things separately when one of them is the primary driver of the cost, the comparative cost to supply the other is negligible and is probably more effort to bill for than it's worth.

I'm not dismissing the vendor lock-in aspect, but I don't think it is the only reason at play.