> It's smaller, so it should cost less

That is... not how the physical world works. The laws of physics hate the large and the small. Or perhaps less glibly parameters do not scale equally. Making a phone is more difficult and expensive than making a laptop for the same reason a 30ft tall human would break their own legs attempting to walk.

To put it another way: A thread rolling screw machine can churn out 12mm/0.5" bolts all day long for a penny each. But if you want to make tiny screws for small pocket watches you're going to pay more (relatively) even though that tiny screw contains way less metal than the larger bolt and the operation is similar. A .00001" error in the larger bolt threads doesn't matter. That much error makes the tiny screw completely unusable. Making a thread-forming die with less than .00001" error is very difficult and expensive and the one for smaller screws accumulates error faster relative to allowable error so must be replaced more often. The steel is just as hard in both bolts but the form of the tiny one is proportionally much thinner.

And similarly if you want a 6m/12ft long bolt you are going to pay a lot more than just the proportional cost of the extra metal because finding machines that can even put that much tool pressure on the dies is not easy. It has to be lifted with a crane. It is just more difficult in every way.

Miniaturization is more expensive. Water and dust proofing is more expensive.

For most things there is a sweet range where cost is lowest and utility highest. Prices go up on either end of that middle ground.