I believe that they are just not used to think about error codes, and by the time they reach the place where they should give them, they already feel like they fully explained the problem, and are therefore even less likely to stop and think about whether they should give additional information.
Asking a question involves a few stages, and they are most logically arranged in this order:
- you need to describe what you were doing
- you need to describe how you were doing that
- you need to describe what happened when it failed (or how it failed)
- you need to give the post mortem report
The post mortem report is where the error message will be, and it is at the very end. By the time newbies reach this point they are at the end of the mental challenge of explaining their problem and are more likely to miss something (for a newbie, there's an information overload problem). Further, at this point they already feel like they described all aspects of the problem, and they have past habits that prevent them from remembering about the error codes: after all, other fields of life have no error codes, so they are not used to think about them.
It may also be that even if they do remember about the error codes, they seem too cryptic to be of actual use. Just what is error 034982? Does this really mean anything to anybody? And does it really add something to that detailed description of what I was doing, how I was doing it, and how it failed? Surly this information stands for itself.