IMO it's because there's a lot of money around, and the places to put it are limited.
Stocks have worked. RE has worked but it will cost you on maintenance. Bonds are divisive. Corporate paper is lame but safe. Forex has been choppy, even though leverage is cheap. Etc.
Really, the amounts I'm seeing people dedicate to crypto are disposable amounts, myself included. The total capitalization of something like btc should be reasonably related to the transaction volume, but it's at the moment impossible to separate the users from the speculators (I consider hodling/wealth preservation a "use").
The issue is not "the price of bitcoin", it is fiat inflation--i.e. the price of bitcoin as expressed in, say, USD. That's one interesting thing about bitcoin, a bitcoin remains the same regardless of price--or at least it will, after all have been brought into existence. One might expect an organic price growth commensurate with economic growth, but who knows what the baseline should be, upon which that growth operates.