The point is to make a monthly donation to show your allegiance to the world’s second-richest man. It’s like a cult membership fee. You get a little graphical badge to show you’ve paid, like a virtual lapel pin.
It was already used as an insult in many parts of the Internet, long before Elon Musk's buyout. It's just the blue check people from that era don't really realize how many people despise them.
Example: https://i.imgur.com/vgzTo5P.png