If you're really trying to serve the outside world, then you want colocation. Cloud providers are way more expensive.
To your point, when talking to your db or [insert shared infra here], then you may want to thinking about real collocation. But it very much depends on your application’s needs - and remember that cloud providers can offer guarantees about which AZ or region you’re in.
With the magic of VPN, I can put my colo box on the same k8s cluster as the rest of my home stuff, in case I want to live dangerously.
Kubernetes is very complicated, but the complexity can be managed if you approach it from the bottom up. Using a cloud service robs you of that ability.
s/Kubernetes/Computers
Other companies hire skilled people that aren't necessarily super-smart, because super-smart people can make a lot more money at Google. So other companies use Google / Amazon, they don't really care what underlying techs it uses, so long as they know they'll be able to hire people with the skills.
If you're rolling your own Kubernetes, you're putting your faith in your own smarts, because you're largely on your own. K8s rewards a certain kind of developer, and badly punishes someone thinking running their own k8s is going to be as seamless a process as consuming GCP resources.