An obvious case in which "all" is not implied concerns 'people.' As in,
Why do people give dead fish handshakes in job interviews?
In most contexts, one would probably assume that the speaker does not mean by the above that all people give dead fish handshakes, because that would be obviously false. So although the sentence is ambiguous, strictly speaking, there's still a clear best interpretation, as follows:
Why does anyone give dead fish handshakes in job interviews?
In other cases, however, the ambiguity causes interpretive problems. When 'people' above is replaced with 'programmers,' the possible semantic range of the sentence is greatly reduced, making the implied 'all' more plausible.
Nonetheless, we can be generous interpreters. Thinking in terms of predicate logic, the statement "programmers give dead fish handshakes" could mean either "there exist two or more programmers who give dead fish handshakes" or "all programmers give dead fish handshakes." These statements can be negated: "all programmers avoid dead fish handshakes" negates the former, while "some programmers avoid dead fish handshakes" negates the latter. So, interpreting generously, it seems likely that the OP meant something like
Why do any programmers give dead fish handshakes?
Or, I think more clearly in this case, its double negation:
Why don't all programers avoid dead fish handshakes?
This still raises the question of why the OP is talking about 'programmers' specifically, when the question applies equally well to all job interviewees. Perhaps the OP thinks that programmers, at least, should have the good sense to avoid dead fish handshakes -- still a generalization, but a more positive one, for programmers at least. Or perhaps the OP was just trying to ensure that the question was perceived as on-topic :)