Code absolutely is a liability. It is not a tool, it's a means to an end.
A simple tool, like a hammer, is not volatile over time. The house that you build with your tools is. It will weaken and rot, and given enough time it will crumble. It takes care and maintenance to keep it safe to live in.
It is the same with code in production; at some point in time in the future, through no fault of your own, the code can become "wrong" as reality changes around it.
Code is also costly to maintain, sometimes even for small code bases. As the world changes, so must the code.
One of the definitions of "liability" in the Merriam-Webster dictionary [0] is "a feature of someone or something that creates difficulty for achieving success". This definition is often met by code.