Back when I played (15 yrs back?) Black Lotus was the consensus "top" card... I don't even see it on that list, so I'm guessing the game has changed a lot...
It's an auto-include. A no-brainer. Everybody wants one. Every deck benefits from having it, and that's why it defeats the spirit of the game and should be left out of future editions.
So, you could say that it's because it's so powerful that it's an auto-include, but then that leads to a discussion about cards that are powerful on their own and what cards are enablers.