My personal experience with such questions is that very often, the process of engaging in dialogue to determine what kind of answer(s) the asker actually wants is difficult and time-consuming. This typically complicated by askers who don't actually show up to the dialogue, leaving people who want to be helpful with no way to figure out what specific answers are helpful. There tends to be no adequate way to helpfully answer such questions, so people try to filter them out as poor uses of time.

The scenario you describe is somewhat different, in which the asker is well aware they have a broad question. Such people are advised to make clear that they know full well it is a broad question and are seeking broad comment on multiple viable approaches.