The Help Center explains the "primarily opinion-based" close reason like this:
primarily opinion-based - discussions focused on diverse opinions are great, but they just don't fit our format well.
Many good questions generate some degree of opinion based on expert experience, but answers to this question will tend to be almost entirely based on opinions, rather than on facts, references, or specific expertise.
The blockquoted text "Many good questions..." is also what we're clicking, every time we select to close a question as "primarily opinion-based."
It looks like Are there cases where vi is the only option? may be about to be closed as primarily opinion-based. It has four close votes right now.
While I can imagine ways to radically alter that question to make it primarily opinion-based (for example, if it had asked for situations where vi is the best editor), I have not managed to think of any reasonable explanation for why the question as Luis asked it is actually primarily opinion-based.
Imagine you're in a situation where you must edit a file. Fill in the details however you like. Maybe there are editors besides vi available, and maybe there are not, but is whether or not there are actually a matter of opinion? (You might be able to contrive a bizarre situation where people would disagree about whether or not editors besides vi are available. But does this arise naturally?)
In order for Luis's question to be primarily opinion-based, things would have to be more extreme than that. The task of determining if vi is available would have to be so subjective and practically unverifiable that answers to a question about it "will tend to be almost entirely based on opinions..."
To a small extent, people disagree about what constitutes an editor. In the sense we talk about text editors in this century, does
ed count? Is a text processing language an editor? This small layer of ambiguity can be explained in a fact-based way, though, and it has been in some comments and answers to the question.
Of course, if there were many practical scenarios where vi is the only available editor, and the different scenarios didn't share other significant common characteristics, the question could be considered too broad. Does anyone think vi being the only available editor is a common situation with numerous unrelated causes? "Primarily opinion based" is the only close reason voted so far on the question.
To argue against something, one must understand it at least a little bit. I'm actually not confident I'm right about this, because so far I can't imagine why four people would think this question is primarily opinion-based. Maybe reviewers haven't been paying sufficient attention, or maybe there are great reasons to think this question is opinion-based of which I'm oblivious, or (and I am guessing it's this) it's something in between.
Is this question primarily opinion-based? Feel free to answer either way, but I'm particularly interested in answers disagreeing with the opinion I've expressed here and stating explicitly how they are consistent with the meaning of "primarily opinion-based" quoted above.
Of course no one is obligated to justify themselves here and now. But it's a popular, well-upvoted question with multiple well-upvoted answers. This is the kind of question that attracts reopen votes.