They created a minimalist, lightweight bell with a massive sound on a mounting system that would allow the bell to be attached to any shape or size of bar without requiring adapters or different mounts.
The price comes (at least partially) from the materials used. Everything is designed to be absolutely ideal for function but also be galvanically compatible. Nothing will rust/oxidise, nothing will degrade (no paint). The bell should last for ages and be able to attache to anything.
That’s the kind of design thinking that should go into everything. It should be built to last regardless of cost.
As an aside, the Knog Oi Lux uses a copy of the Spur level mechanism and uses similar materials – it’s €40 and you have to buy the right size for your bike and it’ll still only fit around something that’s round.