SE has always emphasized specific, focused questions. The model is designed such that every answer is addressing the same question, unlike discussion forums where one posed topic may go in many different directions of conversation. When questions are unfocused, answers tend to emphasize different aspects of topics tangentially related to the question, and it turns into a mess. Closing a question is often used to provide time for the question to be modified and focused before it attracts answers, because it becomes harder to adjust a question once it has been answered without invalidating the existing answer(s).
I disagree wholly with the dichotomy between rigorous homework-like questions and less rigorously-defined original questions. Questions need not be borrowed from a textbook to be rigorous and specific.
I do think that it may be easier to write a question based on textbook learning for a couple of reasons:
Use of appropriate terminology. Learning biology is as much about learning mechanisms and concepts as it is learning language. A student asking a question based on the textbook they are reading may not understand the concepts, but at least they see the words in front of them that are appropriate to use. If askers come at a question without background knowledge and use the wrong terminology, they may introduce things to their question without realizing it. For example, the word "transcription" in biology specifically means making RNA based on a segment of DNA; if someone uses it generically to mean "copy", the question is likely to seem confused from a biologist's perspective.
Many of the people answering questions here have taught courses in biology. Most of the places people get hung up are not particularly unique - we've seen dozens or hundreds or thousands of students struggle with exactly the same thing. That means that when someone asks a question about membrane potentials, I can usually pick up on exactly where they need help even if they aren't perfect at expressing themselves.
That doesn't mean these sorts of questions are better or preferred, just that they are easier to write.
There are additional difficulties with writing questions "from original research and studies", assuming I'm interpreting your meaning of those questions correctly:
Often the person asking the question lacks the requisite background to understand an answer or know what they need. They may be not even wrong in the sense that correcting them really requires re-teaching an entire course or series of courses that people with formal education in biology (even with degrees in other subjects) would already have. We don't expect answers to fill textbooks, and questions that require these sorts of answers are not a good fit for the site.
They may be asking an XY question, where their motivations are hidden by starting not from the practical problem that they face, but from their expected solution. This leads to confusion between both answerers and the asker, where an answer to the question that is written doesn't actually help OP solve their problem, and where the circumstances of the question don't make sense to people who could have answered the actual question, so they end up wasting time critiquing aspects of the question that are not actually important to the asker.
Often 'original' questions are really invitations by the asker to discussion. They don't actually have a specific question, but rather want to learn more generally about the topic or discuss next directions. The help specifically states:
If your motivation for asking the question is “I would like to participate in a discussion about ______”, then you should not be asking here
One of the reasons that we encourage "prior research" to be included in questions here is that it helps mitigate these problems. If askers read about their topic before asking a question, it helps them find the right language to use, identify where specifically they remain stuck, and pose a question in a form that is useful to people with the same problem. Providing context makes it clear that a textbook-length answer is not needed.
I don't see "rigorously defined question in a textbook" vs "a less rigorous original question" to be an appropriate dichotomy. A good question is one with a clear scope and sufficient supporting material, where the asker has demonstrated the thought they've put in (demonstration is key here; it doesn't matter how much prior work someone has done if the text in the question doesn't show it) to constrain what they are asking, whether they're struggling with something in a textbook as part of formal study, or are formulating a fresh idea.