This is a small group of investors selling and making these ridiculous purchases.
It's still an insanely common title.
I remember when Nintendo World Championship carts were selling for $40,000+ a few years ago (before these WATA scammers got involved) and that was by far the most rare and valuable cart... Super Mario Bros is a game that sold 30+ Million copies in various NES cart forms. This reeks of fishy dishonest speculation.