[GreymanTheGrey]

Most of your points apply equally well to ingress as they do to egress. Yet the cost of one is orders of magnitude less than the other.

The only sane explanation for the vast imbalance is vendor lock-in. Everything else is hand-wavy distraction.

[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.