very few built the bit coin mining network. it was all just hackers throwing cpu power at it. however it is to the point where it is no longer cost effective to throw CPU power at it as the # of coins you get is worth less than the power to run them.
The problem of bit coin isn't whether or not it is useful but of it breaking down.
There are 44 quadrillion potential bit coins(21 million to the 8th power), but at the rate at which they are being permanently lost is just as staggering. every time someone loses 1 coin due to a lost password, bad hard drive etc, you really lose 8 potential coins. Real world currencies don't have to deal with "bit rot" (pun unintentional) You lose the combo to a physical vault there are other ways of opening it. even if the physical cash is destroyed you can always print more to replace.
Once a bit coin is gone. it is gone forever. Lastly we are already having to do transactions in milibits. what do we call