Why someone would want to buy the product. Value is in the eye of the beholder, of course, and it’s not always what the maker expected.
A value proposition is the story of why this product or service is worth more to you than the price being asked.
You can think of it as answering the question, "Why does the humankind need this product to exist?"
Very few things can clear this hurdle, and even less so the sorts of things that tend to come up on HN. Very, very few industrial farming topics come up on here for example.
Perhaps a more apt framework would be, "What's the reason someone is giving you money for this product?"
Why don’t people use the word “value” then? Why “value proposition” and not just “value”?
"value proposition" is about how you demonstrate the value.
I assume it's because "value prop" is VC lingo which is a prompt to founders to give their customer "elevator pitch", and we're on community forum that's motivated by VC perspectives & lexicon, so those get broadly appropriated by many participants.