It comes down to cost/benefit of delay on actions with their own window of opportunity and rates of return. If I delay taking actions because I’m waiting for IT services, that’s a real opportunity cost that should be weighed against the higher unit cost of cloud services. It does me little good if I have all this cost effective hardware and software managed internally but it still takes a week/month/
More for a developer to get an extra 5 TB and 100 CPU cores, or to get a firewall rule opened, or to get a new subnet created, or a new DNS zone.
Procuring gear, hiring a team, contracting connectivity, testing, integrating, scaling, etc, takes months. It also presumes you’ll attract, hire and be able to fund management that understands modern processes and can get things done in a timely, quality fashion. Even the best in the business are 50/50 at getting this right, so there will be growing pains. Whereas a top 5 cloud provider almost always has world class practices and processes behind their services and are a credit card transaction away. Much less capital commitment, much less time commitment.
Put another way, why prematurely optimize when you don’t necessarily know what you need long term ? Startups or even new products at large companies need to focus on product/market fit and responsiveness. Their processes and structures should be more like a tent city with gradually paved cowpaths than a planned city.
In the case of a venture funded startup, time is more valuable than capital. In the case of a large enterprise, it depends - sometimes time is more valuable, sometimes operating cost needs to be squeezed. Cloud of all forms (private, public) has become very lucrative in enterprise because of the slow pace and intransigence of IT teams that were assembled in an era where technical and software services could suck and take years to solidify. These days software needs to suck a lot less, and quickly - customers are demanding it. Cloud is not mainly about where you do your computing, it’s about how you do it: on demand, fungible resources, granular billing, API-driven access. I’m sure I can get the costs down if I own all the gear and have a flexibly contracted network, but I still need to ensure I have the automation, processes, and practices that meet the business need for velocity. I can’t risk hiring a team that might put up a ticketing system and manage every request by Excel spreadsheet if they don’t know better.
Building good software means providing developers with infrastructure and tools they need to act quickly with safety, and most importantly, giving them the ability to change their minds without a major cost/capital hit. Cloud (or, as I say above, on demand, fungible infrastructure and rented software) is a major path (but not the only) to get there.