In short because it's the most perfect form of money that has ever existed. Eventuslly mr. Market will recognise this and the market will reflect the true value.
Check out Erik Voorhees' articles if you like to reaf a clearly written explanation why Bitcoin is the best money thus far.
I agree, bitcoin is revolutionary. It IS the best form of money that has ever existed.
However, it is still in its infancy whatever way you look at it. For it to BE money it needs a stable price, who is going to trade with something with no fixed value or at least some what of a guarantee of your spending power down the line. The ONLY way to get round this is to stop all this crazy speculation that it's bigger than Jesus/the internet etc and actually use it as money.
Until it is actually used as money en masse all this volatility is just delaying it being mass adopted. Yes a bubble is great for bitcoin, for publicity and adoption, but it NEEDS to deflate and have steady growth in order to compete as money.
All this bullish sentiment that its value right now is in tripple digits or that it will some day be the global currency is irrelevant. Bitcoin needs to walk before it can run and with the only people jumping on the train are expecting it. The price ends up being 99% speculation and 1% asset, this only helps to stunt its growth as a viable currency.
