Are miners actually selling all earned bitcoins immediately? If so, that means there must be at least 20 million USD "entering" Bitcoin every day in net terms. That seems like a lot, certainly much more than could be supported by actual economic activities in Bitcoin (including illegal ones).

How many people are there who are willing to use, say, 10k USD of their own money for gambling? How many greater fools?

Then again, some of those "greater fools" could be people holding Bitcoin that they collected from ICOs, so who knows.

As they say, the really tricky part of attempting to profit from the bursting of bubbles is the timing.