> Now you need to read new code

And most times it's code that you really don't enjoy reading because it was dragged up from the slurry pits in Beelzebub's own septic tank and mangled over the years into a horrific totem, a paean to insanity, screeching out its perverted agonies the only way it knows how - through JIRA and Kanban boards containing decade-old bugs that you are asked, nay expected, to fix in your first week.

I worked with a contractor who implements an abstraction layer for a communication protocol: goes into a company, provides an integration for the protocol, then leaves.

Similarly I've worked for someone who sets up a continuos integration systems.

There are contracting jobs that don't require you to read the code of others.