I'm glad you're enjoying it!
If you are using the same manufacturer as them, they might have agreed on a lower markup rate with the manufacturer than you did (it defaults to 100% with no contract). You can check their contracts in the Business tab to see if that's the case.
But if you are using a different manufacturer, or even manufacturing on your own, then it could be a difference in the wafer size (the larger the wafer, the more chips are produced, and the lower the unit cost), or in the lithography, yield percentages, etc.
It could be many things really. They might also be selling at a loss. It's part of the AI strategy to do this when lithography yields are still low.