The reason why a lot of the games on itch.io are low quality is because they are made by either people who are still learning to make games or people who don’t have enough time to polish their games (such as in a game jam).
The reason why these types of people post their games here is because the barrier for entry is extremely low: All you need is an email address, no paying for a page like on some other platforms (namely Steam).
Creating high quality games is rather difficult, especially when it is one person creating them like many are on itch.io. Maybe you should try making one yourself before you call other people’s work a “compleat bag of garbage”.