In short, there are a handful of reasons why a card could be worth a lot
Red and white represent Boros and work together to bring out the best of both colors' strengths
Per SKU
Inkmoth Nexus is a colorless, arrives untapped, and can turn into a 1/1 flyer with infect for just one mana
When x happens, draw a card seems to make up a large portion of many recent staples, and more and more legendary creatures with a built in card draw engine get printed and played, so having your opponents discard down to 6 instead of 7 can be a great way to slow down their game plan
Well, if a Contraption would be placed onto the battlefield and it wasnt assembled, or if a Contraption would move from the battlefield to any other zone, it is instead placed into its owners scrapyard (a special graveyard for the Contraption deck)