I have seen smaller RoR, Django or lampstack apps being deployed on kubernetes exactly for reasons you mentioned. It is often pitch as a silver bullet for the future.
When Boss says "my idea is gonna be HUGE, so make this go fast", you can either spend 4 hours optimize some DB queries, or you can spend 40+ hours in a broadly scoped "conversion" project and have a new thing to add to your resume, and then spend 4 hours optimizing some DB queries...
One of the worst, bazooka in knife fight moment was when I interviewed for a company that was a medium scale direct to consumer streaming service that was built some custom resource to create one pod per user, their worst case scenario was where they would have around 1000 concurrent users.
I worked in a Python web-scraping team doing 3 million requests per day. Their solution to manage concurrency was also one pod per crawl, each with its own DB connection. It really struck me as crazy that everyone thought this was a good idea.
Strikes me as someone buying a massive SUV, to only use it to move one bag of groceries from the store every week. Some day in the future they might suddenly have a family of 6 to feed or have to haul a boat somewhere, so better get the big, overkill car.
I have personally experienced the other end of that problem, and it applies just as well to the k8s discussion. When all the kids are gone it's hard to admit you're not a soccer mom anymore and adjust to grandma mode. It can be a hard thing to trade in the Suburban for the Lincoln. Oh wait, Lincoln's aren't the cool thing so much anymore. That whole world changed while I was driving Suburbans.
This describes ~70% of adults in the southeastern US.