Because every few months people realize that no one has delivered anything.
(1) BTC has not delivered mainstream users.
(2) ETH has not delivered any useful apps with a meaningful user base.
(3) XMR has not delivered any significant Dark Market volume.
(4) FCT has not delivered any revenue and insiders are selling.
(5) STEEM is down a full 90% with an abusive model based on 12th century Feudal System meets Hunger Games.
(6) NAV has delivered precisely zero anon.
(7) Another "reputable" Top 3 exchange is "hacked"... and then proceeds to openly swindle their Customers.
Etc, etc, so traders take their speculative profits... and wait for the next train...
Except the long-term losers in this Zero Sum Game = bagholders with "strong hands".
1.But bitcoin is trending at the moment . did you mean ETC
2.it is just a gas project from the beginning
3.what difference does it make if it has a significant Dark Market Volume
4.Steem is just a Ponzi model