I agree and I'm always surprised to see how complex the backend of very simple businesses are.

I'm always amazed to find 10 Infra engineers and 15 backend engineers to maintain a very simple webApp for example.

I feel like as soon as you have more than one program to manage, you need some sort of orchestration. You could build your own that's simpler than Kubernetes, or you can just click the checkbox on your cloud provider and not think about it for a long while. Type in 10 lines of YAML for a Deployment and maybe a LoadBalancer if you're feeling adventurous, and your app is deployed. Need another replica to deal with increased popularity? Change one line. Split up some code into another app? Just kubectl apply another deployment.

There is certainly overhead (kubelet, master) over running your PHP app on bare metal or whatever, not to mention having to figure out what deployments, pods, services, kube-proxy, etc. are... but once you've done that, it's pretty easy. Especially if you use something like GCP, you don't pay for your master, and there is a web UI for doing everything that's simple. I would recommend it once you need to scale beyond 1 computer.