Sure, you don't have to use k8s. You can roll your own solutions to what it solves.
Your own custom built solution will work, but what in 5 years? 10 years? When it all becomes legacy what then?
Will you find the talent who'll want to fix your esoteric environment, just like those COBOL devs?
Will anyone respond to your job posts to fix your snowflake environment. Will you pay above average wages to fix your snowflake ways of solving problems that k8s standardized?
I bet your C-Level is thinking this. What's to say they won't rip out all of your awesomeness and replace it with standard k8s down the line as its dominating the marketshare.
When you're laid off in the next recession, is your amazing problem-solving on your snowflake environment going to help you when everyone else is fully well versed with k8s?