First thing to admit in the bitcoin world nowaday is that bitcoin isn't what it was created to be.
Bitcoin was originally created to be an anonymous currency, with immutable transactions, freeing people from the dictatorship of the banks.
Amongst bitcoin enthusiasts, you can find original bitcoin users, aiming to spend it and use it like a genuine currency. But the majority use bitcoin as a pure speculative product.
The more we hear about bitcoin rising price, the more people want their piece of the cake "ok I want to invest it that too, I want to make a money and it looks like a nice increasing value", adding to the demand. I don't think the price of bitcoin will decrease anytime soon because we are still at the beginning of the curve of adoption, as we can see on, for example, google trend :

My guess is : at each peak, bitcoin earns new users, making the price rise. When they have used all their "potential of speculation", price decrease. We can see on the chart that we have had a huge peak of attention, and coinbase and other trading platforms confirms it, bitcoin has a lot of new users.
It looks like a Ponzi scheme because, when every potential bitcoin users of the population will have exhausted all of their "potential of speculation", there will be nothing left to sustain the price of the bitcoin.
Our "only" chance is that, in the ~2 comings years, huge actors like amazon, facebook, even governments, doesn't obstruct to bitcoin (like china did) but instead start to give bitcoin credits as a proper currency and not as a stock product (like it is happening now).
TL;DR : I really do hope that amazon will one day start to accept bitcoin

A little nitpicking. BTC was never anonymous. It was this compromise from the ideal that allowed BTC to be created n the first place.
Another nitpick - there isn't a relation to a Ponzi scheme. If anything one can compare it to a pump and dump, but it's way past that stage now.
People aren't spending much now primarily because they think it's going to go up in value. That will change. The price will level off.