Scarcity

Bitcoin could possibly be the most scarce asset on earth. There will only ever be barely 21 million bitcoin in existence. Taking into account its decentralized nature, and its immutability, and the inert nature of its protocol development its hard to see this ever changing. With over 7 billion humans on earth, there are not many to go around. fortunately each of those bitcoin can be broken into 100,000,000 units called Satoshi.

Unlike gold when the demand for bitcoin quickly rises, the miners cannot just increase the supply in response to increased demand. There is no way to just mine more bitcoin in response to demand. This dynamic along with bitcoins schedule of diminishing mining rewards will contribute to its rarity as adoption grows. This could produce a market cap many multiples of where we are today in a short period of time.

Many of the altcoins have no coin cap, or have such weak security model that the cap can be changed by decree.

These properties are conducive to the bitcoin network being a great store of value outside the traditional monetary system.