Do we need to explain why we are asking a question on philosophy.stackexcange?
I ask because I think that's why this question generated some annoyance.
Clear motivation of philosophical context is a pretty good indicator that a question is topical, specific and study-derived. Great questions for this site are not just those pertaining to philosophy construed broadly, but are rather very specific cases of some particular problem arising from individual instances of philosophical study.
To my mind all this is most-easily navigated by having a bedrock anchor of some theoretical work or writer that you are actively working/thinking through philosophically to ground the question in some technical philosophical context, which provides the means by which an answerer could indicate not just a solution to a problem, but an indication of why this is persuasive philosophically-speaking, as well as indications of what research would show the answer to be well-founded.
Providing clear contextual background (as to why the problem has become interesting/important in your study of philosophy) is not just matter of courtesy to would-be answerers, but also enhances question quality dramatically and improves the likelihood of getting a great answer, by specifying as closely as possible, hopefully with specific references, what the relationship is between your question and the specific philosophical texts and thinkers you are studying.
No, you should not need to explain why you are asking a question.
To the contrary, the objective of the question should be evident from the question itself.
One of the major close-reasons all across SE is:
unclear what you're asking
Please clarify your specific problem or add additional details to highlight exactly what you need. As it's currently written, it’s hard to tell exactly what you're asking. See the How to Ask page for help clarifying this question.
One of the dead giveaways to questions which are subject to closure under this rubric is when you have no idea what a good answer would look like, or what information would be helpful to the asker.
Now, adding background information on what motivated the question may provide context and in so doing guide answerers in providing helpful answers, and personally I make a habit of it when I ask questions on SE, but it is not required.
What is required, however, is a clear question with a clear purpose. Any question which invites a free-for-all is subject to closure under the reason given above.
This isn't a pungent dorm-room hosting free-associative conversations, this is a Q&A site. Here, we do philosophy, not philosophizing.
TL;DR: when you ask a question, you have to have a very clear idea of what you are looking for, and then include enough detail in your post to communicate that need, explicitly and unambiguously.