Why? It's just because people is scared to lose anything that they gained and I dont think they will hold something that their value is not stable and it is really affected to someone who hold so many btc. Let's say that you hold 1000 btc and suddenly the price down a lot did u want to save that again?
Thats why I think bitcoin can't be invested for a long term
I think the OP meant in the first post that your investment will be tied to the current USD value using a 3rd party bitcoin exchange to offset the falling price of bitcoin If I understood this right If you turn the bitcoins to cash and hold it under the mattress you won't get any more and the bank interest rate isn't a lot either.