> since they are experts

This is the engineering perspective, not the finance perspective. As an engineer holding an MBA, I've made the argument countless times in BigCo to move from cloud deployments to on-prem. When you're a startup, you often simply don't have the cash on hand to make the capital expenditure to build out datacenter capacity, especially with an uncertain (but hopefully high) expected rate of growth. When you're a BigCo, the script flips; you have plenty of cash on hand and you want to improve overall profitability, which is done by using capital expenditures to reduce operating expenditures, i.e. funding datacenter build-outs to reduce cloud bills.

> experts

Companies can hire experts and can still out-source to colos if they prefer. This is a question of political will and risk analysis.