Because they are funny. I think you have a meme anti-bias here.
I don't have any problems with memes being shared. It's the monetary consequences from sharing that bugs me as these can be used as a front to just milk some votes. If you think they need to be rewarded, there's always the tipping feature. I'll just state in the rules that meme posts be set to burn rewards instead of decline rewards so that curators can still get curation rewards but the author who shared the post doesn't.