Because it mustn't "just work" and then when the project grows you setup something new. It must "just work" and then scale to continue working for the initial and maybe all phases of the software product.

So e.g. security matters, so you rally don't want to maintain an OS. Sure a OCI image has OS like properties, but by using stateless approaches and carefully select a very thin base image and rebuild it automatically with the newest version of the image you can sidestep most of that work load.

Then you need auto scaling.

Then you need to be able to add services on the fly without problems (e.g. another DB) and they need to have their own scaling.

Then there is networking, as you don't create a super complex applications you don't need anything complex but still something solid.

fly.io does provide all that

So not only can you get something running trivially, you can the incrementally improve on it and even ship it in many cases without needing to re-design your deployment.

Looks tbh. pretty grate for small and mid sized companies (or autonomous project of such size in larger companies).

But if I'm going to do all that, I might as well just install k8s and deploy with the cli. I've already gone through the learning curve. But I don't want to do that. I don't want other people that might join my project to have to learn k8s for a tiny side project.