I think that is because the world of cryptocurrency is still pretty much underground. Despite the popularity of bitcoin, the common public only really "
know" about it but not actually
understand it.
Moreover, the whole process of how bitcoin achieves its value is hard to understand and too complicated, even for educated people (unless they are into economics and cryptocurrency).
As
insto said:
...Its value is determined by the number of people or business units that accept Bitcoin. If more and more use, the value will continue to increase. Conversely, if it gets less, the implication is that the selling price will go down. Besides that, as a crypto currency, Bitcoin does not recognize transaction cancellations. The process is also public, no entity can provide guarantees for negligence that causes loss or errors in the shipping process. Hardware wallets (special devices for storing private keys) are also susceptible to virus attack or damage if not treated properly, can cause coins to float.
There is no legitimate back up for bitcoin, unlike normal national currencies (which have values depending on the government's gold stash and many other economic factors). It mainly depends on transactions and how many are really willing to use it.