True, but only a minuscule fraction of it is used for that purpose. If that were the sole source of its value, it would be worth pennies per once.
If it wasn't radioactive, poisonous and pyrophoric people would probably all just leap into the Neptunium market.
If it were only worth pennies an ounce, numerous industries wouldn't be paying what they do for it. The fact that many industries value it at several thousand dollars an ounce is self-evident from their continued use of it.
Some bitcoin advocates will talk about how useful it is as a currency, and I wonder how much bitcoin is actually used for purposes other then to hope you can sell it to someone else for more than you paid.