Basically because of miner's fees. Transacting in Bitcoin wasn't profitable, because miners got together and raised their fees so high that it wasn't worth trading Bitcoin.
Miners don't set the fees. A miner will include the most profitable transactions in a block, and a user will pay a higher fee so that their transactions are mined sooner.
So, there is a flaw in Bitcoin. I did a low fee exchange when the fees were high. Then the fees came down to lower than my fee. But my transaction just sat there. It still might be there if I hadn't pushed the people to whom I sent the coin.
We don't need fees. If the miners aren't getting enough from the coin they mine, they can sit on it, and supply and demand should raise the price. At least until the people stop trying to make trades.
