One of the first things I do in a codebase is get some working IDE/editor up where I can quickly run the program under a debugger, even if I'm not immediately troubleshooting something. It's never long before I need to use it.
I was baffled when I too encountered this. Even working collaboratively with people they'd have no concept of how to use a debugger.
"No, set a breakpoint there"
"yeah now step into the function and inspect the state of those variables"
"step over that"
: blank stares at each instance :