Why does it seem that on larger platforms there are bots that downvote comments?
You can tell it’s bots because all the downvotes happen at the same time. I can guess for astroturfing purposes one would want to upvote their targeted comments and downvote all others but on lemmy?
The instance admin can see votes. If you are noticing a pattern maybe ask them to confirm? There can be delays in federation so you might see them all come in at once even if they occurred quite a bit earlier.
I know your question was “why” but maybe confirming that is that is happening vs a different cause can be the first step.
I’m convinced its often the admins that the bots belong to.
Everyone can see votes: https://lemvotes.org/
Unfortunately it doesn’t work, returns 404 for everything
It has definitely worked for me in the past, maybe it broke recently :(