Given that the value of crypto is notional, the question to ask would be- Why is Bitcoin (And others) still gaining investors and users by the hundreds?
The answer to my mind would be two things
Constructively- People have come to trust these currencies as being carriers of value. More over they treat this as a hi-tec asset, maybe risky, but still an asset.
Negatively. Bitcoin and crypto-currencies represent something out of bankers' reach. Bitcoin could become the "Batman" to the villainous Jokers- the Banks and the Central Reserves which have completely fallen under the control of the elite. This is not only a hope but an increasingly popular opinion.
One more aspect is currencies like Steem, which generate value in a new way.
Lastly I like to think of Cryptos as diamonds and rubies. What makes them valuable but popular opinion and limited availability!! 
@juanmolina be cautious surely. But to compare this to the dotcom bubble is overkill. Nobody is throwing money at blockchain by the bushel, in fact cryptos have flourished in stormy financial weather; and this indicates a sound support base.
Keep Steemin!!
Greetings dear friend @sarez.
Thanks for this amazing comment.
In my opinion, the growth of BTC is supported by the great confidence that it has managed to sow in the investors. Remember that in the beginning nobody believed in BTC. It has been a work of 10 years to establish itself and achieve to define itself as a real asset.
In general, the crypto looks like a safe investment. But falls in prices like the one that occurred last year, made more than one investor tremble.