Is there any reason why some people rate stuff as garbage when it is not?

Could be:

1) Trolling (when mean people rate things low just for fun).

2) Are your images/videos etc credited and keyworded? Because if they aren't, lots of people will rate them low.

3) Someone may not understand the rating system. For example, they may think that a rating of "1" 星, 星级 is the best rating that they can give.

it depends, people can be stingey when it comes to comments, titles, crediting and keywords.

but 更多 likely TROLLS!
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