As an individual engineer, I think it's inherently valuable to make my projects easy to hand off (in addition to as maintenance free as possible). The company is less impacted if I leave, sure, and it also means I can take a vacation without constantly getting messaged. Long term, it means that I end up working on more bleeding edge "cool" projects, since I'm not bogged down with years of making myself irreplaceable, and folk want new work to benefit from the same level of redundancy and maintainability.

I believe that I have a perception of being irreplaceable, but it's because of my future value rather than past value.

I've never felt like I was being treated like cattle at work, though, so maybe I've just been lucky enough to work at good companies.