Many people don't have the luxury of write and jump ship. The vast majority of my career was not greenfield development. It has almost all been maintaining pre-existing software. Some of which is more than a decade old.

The challenging part of us in the software maintenance job is to balance a need to refactor with a need to add features. It colors your opinion about a lot of things. You start to evaluate methodologies, technologies, frameworks, and even library choices by their impact on long term maintainability.

I frequently find myself at odds with a primarily greenfield developer in tool choice because I'm looking forward into the future and it doesn't look pretty.