There is a very big gap between IaaS and PaaS. K8S is an abstraction on top of VMs so you can have a customizable PaaS that runs on YAML code. It has nothing to do with how complex your app is because K8S is about running it with less work in a declarative fashion. I'm currently in and have worked with dozens of startups that have saved lots of time by removing all the ops overhead with K8S because it runs the servers and we can just deploy our apps.

It seems like most of the problems are actually about installing and running K8S software itself, but then 95% of companies won't be doing that and using the managed offerings instead. This is no different than companies using the cloud over running their own DCs.