As someone's that maintained deprecated services, I can say that's easier thought than done. Each piece underneath you will eventually ask you to migrate off it, for any number of reasons: It is deprecated itself and being removed, or it has a bug that was fixed in another version, ... Then the replacement / new version won't support all your use cases, so you need to coordinate with them development of that support.

And this is all only about code, not about the cost of keeping the service running with good availability on old infrastructure.

The TL;DR is: Maintenance is never free.

This. Parents comment is typical of management, and frankly I applaud Google for having the confidence to ignore it rather than incurring all of the technical debt.