Because they do not think in exponential terms. The human brain is just used to think in linear terms, exponential rises take a lot getting used to.
But bitcoin? It was rising exponentially for a while, and now it entered over-exponential territory.
This means that in the logarithmic chart we don't have a line any more, but a parabola.
That is why the time for a doubling of the price will get shorter and shorter.
I drew the logarithmic trend channel and these are the possible reversal zones:
1. st at around 25K
2nd at around 75K
3rd at around 145K
If the full move is done, we could see, and I now it sounds insane, 145K until the end of march 2018.
I think 25K is the most realistic scenario, with about 60% probability. Timeframe: December-January
75K with 30% (timeframe: end of february), and 145K with 10%. It's just an estimate, but it's good to know these important resistance lines.