To name a few:

K8s really kills the urge to say “oh well I guess we can just do that file onto the server as a part of startup rather than use a db/config system/etc.” No more “oh shit the VM died and we lost the file that was supposed to be static except for that thing John wrote to update it only if X happened, but now X happens everyday and the file is gone”.. or worse: it’s in git but now you have 3 different versions that have all drifted due to the John code change.

K8s makes you use containers, which makes you not run things on your machine, which makes you better at CI, which.. (the list goes on, containers are industry standard for a lot of reasons). In general the 12 Factor App is a great set of ideas, and k8s lets you do them (this is not exclusive, though). Containers alone are a huge game changer compared to “cp a JAR to the server and restart it”

K8s makes it really really really easy to just split off that one weird cronjob part of the codebase that Mike needed and man, it would be really nice to just use the same code and dependencies rather than boilerplating a whole new app and deploy, CI, configs, and yamls to make that run. See points about containerization.

K8s doesn’t assume that your business will always be a website/mobile app. See the whole “edge computing” trend.

I do want to stress that k8s is not the only thing in the world that can do these or promote good development practices, and I do think it’s overkill to say that it MAKES you do things well - a foolhardy person can mess any well-intentioned system up.