“When looking at Game of the Year, there are multiple factors to consider: critical reception, general consumer reception, and popularity. There are other variables that can be rolled into the methodology, but for the most part, this is the trio making up the formula. A popular game doesn’t always mean a great game though. Millions buy Madden every year, but they all insist it is more torture than entertainment. High review scores aren’t the sole determiner either. If a game gets ultra high review scores, but only 50,000 people play it, it’s hardly relevant. Further, critics aren’t the only consumers of games, so general consumer reception is also important. As for why only six games? It is simple: that is how many games were nominated for the category at The Game Awards last year.”
Source: N4G PC Astro Bot and the 5 Other GOTY Contenders So Far