Usually everyone can rate and there are a minimum number of ratings required in order for you to able to get ranked. From +- 10k entries, there are probably 'only' going to be around 2k submissions - most people have already given up and abandoned there well-intentioned projects. In a previous jam I have seen people come close to winning with just 12 ratings, and others around the same mark with over 100 ratings. Itch will work out the average but its based on that minimum number to arrive at an average score for your game.