That’s not necessarily true. Different large firms have different use cases.
I have worked with Flipkart in the past where we had our own data centers. It’s cost-effective when you are a very large firm but you have to develop a lot of tools in-house and purchase 3rd party subscriptions for tools that you’d get by default with AWS etc. It saves you cost but it makes running the business tough and there’s pro and cons.
Large companies like netflix etc still use AWS despite having the best tech engineers only because they want to focus on the core business/tech and not managing infra. And you’ll very rarely see large companies moving away from cloud providers to their infra indicating it’s a better solution for their business