What is the value of providing speculative answers, partial answers, or answers (usually uncited and under-supported) in comments? These are comments that the author was not confident enough to propose as a voteable answer. In what way are they valuable as comments instead?
Why do people do this? Because of lack of confidence, clarifying whether this does indeed answer the question in such circumstances. Often it might be because people think the answer they are thinking of is rather obvious or trivial.
While it may not be ideal, I don't think these comments have no value. They engage with the question and can provide clarification to the OP and to other people considering an answer.
I don't think we want to discourage engagement with the question by somehow banning such contributions. Sometimes people reply to these comments, saying "I would make that an answer". Encouraging people to upgrade comments that appear to be a good answer is an appropriate response.
You seem to have a fundamental problem understanding that comments are not answers.
The value is that this community will end up respecting the comment poster with a hunch more than someone who posts an answer that wastes people’s time.
Value of speculation, answers, and partial answers in comments?
The value is someone is not confident enough to know what the actual answer, or is making a hunch. So a comment is a way for someone to present their ideas to the question asker without running the risk of down voting.
In many cases when someone gets clarification or confirmation regarding their comment they will take that comment and flesh it out into a full answer.
The value can clearly be seen here in your own answers. I do not have enough rep to see deleted answers, but I know you have engaged in this behavior where you have purposefully added many answers that should just be comments to questions on the main site.
This is clearly exemplified by your own meta question here:
What is the official etiquette on answering a question twice?
When you have two distinct answers, it's better to post two different answers than to put them both into one answer.
Does Movies & TV adopt that approach?
Perhaps there is a language or cultural issue at play with your engagement with this community. But they way your yourself seem to have been posting comments as answers is disruptive and not a good use of the way Stack Exchange sites work.
An “answer” is typically something that has actual references and such that directly address the issue and the answer itself will often contain quotes from the sources in the text of the answer itself.
For example, there is definitely a deleted “hunch” answer in this question I posted. After many comments explaining this to you instead of editing the other answer, you simply posted a fully new answer. And that “answer” is not a good answer at all.
While you cited multiple sources in said other “answer”, the answer is ultimately a comment. The first line of this is a comment, “There is no definitive reference in the film to the age of the character Naru.” And then the rest of the question basically cites reviews and other pop-culture magazine features from third parties about the film.
None of that is an answer. Thus the downvoting.
In general, you yourself need to first post comments for clarification and only when it is clear that the comment is an answer that you then post the comment as answer.
Again, you routinely have posted comments as answers. And doing that is disruptive and not a good use of the way Stack Exchange sites work.
The value of comments is you show respect to the community and the question asker by not wasting everyone’s time and effort by posting content that is not useful.