Greenlight is simply a question for each user. Would you buy this game? If no then you should click no. No matter the potential of the game. Steam wants to know if YOU want it. So if you don't vote the game will keep popping up in your feed. So you either have to vote yes or no to make it go away.
That is why downvotes doesn't matter on greenlight. Because it doesn't mean something bad. It just means that this person wouldn't buy the game. So if a game have 100 000 no votes and 10 000 yes votes the game will be greenlit because steam expects that 10 000 would buy the game. (I know that the ones who end up buying it would be far far less )
Anyway. That is how greenlight is meant to work but people are obviously not using it seriously all the time
In spirit that's how its supposed to work, but if you track games on Greenlight, a lot of NO votes = never get greenlit. There seems to be some kind of threshold where Valve curators flag the game to not pass, so it can stay there for years.
If you look at the database site I posted the URL to in the earlier post, you see some games in the top 300 that have been there for ages, they have enough yes votes to be on top of most games, but they have a ton of no votes and so they just remain there.
It is very rare for a game with <30% yes/no ratio to be lit, in fact for the past few months I haven't seen a single lit game with a poor yes/no ratio.
There's the theory from greenlight devs, when you submit the game:
There's a chance a Valve curator sees it, likes it, and it gets in the queue to be lit regardless of votes. This has happened for a few games in the past months.
Other games have to get enough yes votes to make it to the top 300. Once in there, the curators take their time to go over each submission and judge whether it passes or not. Obviously in the top 50 gives your game priority to be examined, but they do get around to the others outside the top 100-300.