Well that 24/7 db server is not going to back up itself and maintain itself when the HW fails or the power goes out. This is not trivial/cheap to assure and maintain. Likewise with hosting your own S3. The value is not in the HW really (and the cloud providers know this when pricing).

I have this setup on AWS and look at "bringing it home" every year but the nightmare of having to assure a good level of availability is not worth the saving of a few extra $1000 per year for us at least. Completely different issues not related to your HW can happen, your office internet simply goes down or power goes out while you're on vacation etc..

At least there is major competition between a lot of cloud providers nowadays so nobody can get away with insane prices anymore. Though, would be cool to see some kind of standardised price comparision metric for medium/high complexity cloud setups. Sort of how you compare grocery prices, you have a standard purchase list.