These are all secondary though. The original, base-level reason Bitcoin has value is that perfect record-keeping has value and energy has value, and the exchange of energy for perfect record-keeping can only be settled in bitcoins.
Discussion
Why not some other crypto?
For example, take Bitcoin, change the code to recognize a new Genesis block, make no other changes and bam - Bitcoin 2, with exactly the same properties as Bitcoin.
Obviously this cannot have value or Bitcoin is not really scarce. But every *objective* argument for Bitcoin applies fully to Bitcoin 2. Only temperamental arguments about the pre-existing network effect (and the like) can distinguish them.