Because they are funny. I think you have a meme anti-bias here.
Just because a joke is short doesn't mean it's not funny.
For people following a series, memes are enjoyable and sometimes useful. Here is an example:
This made me give it a second try to the latest Date A Live season regardless of how shitty was the previous one. I dropped this anime after the second episode, but I picked back up, thanks to that meme. And yeah it has nothing to do with Hive.
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.