But expectation can be different to real experience. For example, I thought I won't enjoy Disco Elysium and Wildermyth but I did. On the other hand, there are some games I thought I'd enjoy but I didn't.
Its your call, of course, but I just think its weird to vote for something you haven't actually experienced.
It's more an issue when people vote negatively for something they haven't played yet, and since The RPGCodex puts a value on negative voting in their polls, they instil an atmosphere that it's immoral to vote for something you haven't played. And they need to do this because the prevailing culture there is to shit on things.
RPGWatch is different because we're only interested in assessing which games made people happy. We don't care if 50 people loathed Dragon Age 2, if 10 people really liked it then it charts.
And let's say, for argument's sake, Dragon Age 2 came out on 1st December. We all know and are accepting of the fact that this site has a number of absolutely rabid Dragon Age fans. They could release a 3 hour game of a bunch of NPCs nattering to each other and then you kill a dragon & it would get votes at the end of the year.
So 1 month isn't a very long time for the rabid fans to all have played it. One or two of them could well be just too busy over December to even watch one episode of Jar Jar Binxs the Musical, a Disney+ exclusive serialisation, let alone a 3 hour Dragon Age game.
But it's still blindingly obvious that they will be playing it relatively soon and will have voted for it if they'd had the time. So, because this site caters to everyone, from casuals to pro-gamers, it stands to reason that leeway is acceptable for people to vote in advance of what they plan to play and very likely enjoy.
Whatever point in time you schedule for a vote, there will always be people who are nearly ready to play something but not quite there yet, and as such any too-strict method of evaluation will disenfranchise someone from the process.
Since our vote is about what made us happy this year, then, for sure, the happiness of hope and expectation of a game that was released this year has indeed provided someone with happiness, vote-worthy happiness.
Sure, if in the unlikely event of them finding that they regret the vote down the line somewhere, that's certainly a thing, but it still doesn't eliminate the objective fact that the game provided them with a lot of happiness in its year of release.
As someone who at one stage left this site and preferred to post on the codex for a while, this is all probably a mindset that would indeed seem a bit alien to you, but I hope this horribly long post of dreadful mansplainin' at least allows you to solve the "I don't understand why" aspect of your confusion, regardless if it changes any minds or enables you to approach the two sites differently.