That depends on the skill and experience of the developers that make games. You have the famous developers such as Krin and John that make great, addicting games, and then you have the unsung artists that are honing their skills, whether their games are getting low ratings or not.
This is why we create reviews and why the team encourage reviews, so those developers can understand what the people want and what they are doing wrong (and good!). If there is a game that catches my eye (not too often unfortunately), I will try to create a review for him/her.
that is a really great remark and i completely agree, that's one of the reasons i like this site is because it's sort of like healthy criticism and helps you become better at making games and maybe go professional like John (makes my favorite games) but it's all just practice, and practice will eventually make perfect.
A lot of the games are very fun! Especially for free. I am surprised at how the ratings are for some games though. Like I think a lot of 7 games should be at least 8's and a few 8 games could fair as 7's.
Anyway though to me it shows that there are already a lot of great games and game designers on the site, but I get what your saying, having more great designers couldn't hurt.
All games can improve. But why improve a game when you can make a new game that's better? A lot of Devs on AG don't look at the reviews they get as well.