Technology. More specifically, new "public ledger" or "blockchain" technology inspired by Satoshi's implementation of bitcoin. This is what it looks like when a new important field of technology comes into being.
I'm guessing most gains are from increased demand due to investor speculation.<p>When you look at the crypto usage for practical purposes there aren't too many yet. That tells us it's mostly people buying and holding.
The magnitude of the boom is likely a speculative bubble. The reason there <i>is</i> a boom of any size is that many more people are working on blockchain applications now.