It has three high power voltage converter circuits which are needed for it to support USB Power Delivery. Those are more expensive than the batteries and no other device has three of them.
Lithium-ion packs are measured at 3.7 volts, not 5.
Buck or SEPIC based DC/DC conversion systems absolutely do not cost more than even a single LiIon cell. And to have multiple converters is far from a novel concept.
I think this is a neat implementation but there is no technical justification for this price tag, and the idea is far from unique. Looks cool though, and I guess for some that's all that will matter.
Lithium-ion packs are measured at 3.7 volts, not 5.