Arcum Dagsson was among the first Commander cards to have a very high foil multiplier, and his power is well known to players of the format. Non-foils have been relatively cheap for the most part, though this week they saw a significant spike.
As more artifact synergies enter the format, Arcum only gets better over time. I'm sure many players are excited to pair him with Breya, Etherium Shaper. This isn't the first spike around the latest Commander release, and it won't be the last.
Keep your ear to the ground for good Commander specs. This is a great time to absorb popular Commander content in search of cards poised to spike. The new Commander release coupled with the holiday season and general disinterest in Standard all points to players spending money on their favorite casual format.