I think a number of factors add up over a 3-5 year timeline (obviously this will be more or less true for different organisations). There is the way the cost scales for a given instance in the cloud - in the old days, for example, doubling the memory or doubling the CPUs didn't double the cost of the kit, but it does for clouds VMs.

Another example is that the cloud bills you for everything, in the old days I could have a database server on a network and query it as much as I liked, the cost was fixed upfront for the lifetime of the hardware. Whereas it's very cheap to get started with a managed offering but e.g. BigQuery charges you for every query, Cloud Functions charge you per invocation, bandwidth is chargeable etc.

Speaking of hardware, in the old days you could look at your hardware and say, actually, it's fine, we don't need to upgrade/replace it this year after all, and it will just keep running. Whereas in the cloud the payment is continuous (perhaps offset by the fact that it's easier to "give back" excess capacity).

There will come a point at which the cost of DIY vs cloud will cross over, the question is whether you will reach that point, and if so, what you will do about it, since you may be well and truly locked in at that point.

You always can drive cost concessions from sales, especially for base workloads where you have time flexibility.

For a big company, cloud rarely saves money for many categories of expense. In a normal market, it is almost always faster time to market to rent, and always cheaper TCO to own.

This is a different market and one which is ultimately constrained by the availability of land. Notably, cloud prices do fall especially relative to the compute power. Specifically I remember when Fargate moved to firecracker and prices fell by like 40% or something similarly considerable.

Maybe managing your own internal cloud is indeed cheaper (especially if you don't account for support or maintenance!), but arguing that cloud prices don't decrease or making some housing analogy seems like poor reasoning.

It’s always better for you as a person to rent box truck to move. If you’re a company that needs a truck 3-5 times a month, there’s a probability that leasing may make more sense.

I’d say that businesses that suck at managing on-prem will not magically get competent in a public cloud.

It takes time to build a competency. If you have to figure out how to operate everything from the hardware and networking all the way up to application, then you might very well fail as a business. If you can pay Amazon to manage your networking, hardware, databases, managed services, etc while you work on your application-level competencies, you stand a much better chance of succeeding ("I don't know if I could build everything from the ground up, but I can probably fumble my way to a container image"). As you become very proficient, you can cut costs, and if you're super proficient you might get off a public cloud altogether or more likely you'll just use that as leverage to negotiate a lower cloud bill.

Interestingly, you don't hear about many businesses that are so competent that they move from the public cloud to their own private clouds. Some people will shout "Lock in!", but I don't buy that--I've migrated between public cloud providers before and it's work, but if you're competent enough to run your own private data centers then you're plenty competent enough to migrate to them.