In retrospect it seems obvious, but back then, the most optimistic talked prices around 4$ (we got to 7$ in what, two months?) . Anyone posting suggestions of 100-200$ was just like the guys now, talking about 10,000$ in 2015.
Its easier to go from $10 to $100 then from $100 to $1000.
It needs much more volume.
We are far from saturation. Assuming bitcoin will replace fiat, the road from $1 to $10 should be just as hard as from $10 to $100 but at some point this would accelerate as fiat can be printed at will. If it were limited I would agree there would be exponential growth until bitcoin economy is about 10% of fiat economy and there it would have to slow down but if bitcoin takes over the world, you will see 1BTC being traded for 1 trillion USD easily. By that time there might be million dollar bills in circulation that the US.gov promised to back with 1µBTC each and depending on whether people believe it or not, the decline of value will continue.