There is a hype cycle because the supply gets cut in half, and people who trade know this and make money off the fact that the supply will be decreasing.
Think about it....You know for a fact that in 4 years time there will be 50% less bitcoin being mined each year, and then 4 years later, again 50% less, going on and on forever. Even if there is no more demand than there is today, when you cut the supply in half, but keep the same demand, the price should surely go up a lot. People who trade bitcoin know this, and they start buying up bitcoin in advance, with the purpose of selling it later at a big profit. This causes the hype cycle to repeat itself over and over, with higher highs, and higher low prices too.
It costs so much, because there is so much demand for it. If nobody wanted it, the price would be zero, but everyone wants it, and the demand is reflected in the price.