Why?
People tend to focus solely on the demand side, saying things like "it would require too much money to hold the price up" at six figure valuations. But price isn't determined solely by demand; supply also plays a crucial role.
What happens during bubbles is that supply dries up. The ask side completely disappears across all exchanges. So it takes very little money and volume to push prices exponentially higher. That's how bubbles are born.
Is that sustainable? Probably not, and that's why bubbles pop. But that doesn't mean we can't see six or even seven figure valuations first.
The main reason why it can't happen is the fact that we are talking about people who got in from anywhere at around 10k to under NOT to sell until it is 100k. You are aware that people do tend to sell even when it reaches above 12k and you are asking or at least expecting them to not sell when it reaches 20k? Or maybe 30k? Or how about 50k? noo, you expect them to sell at 100k?
You are ignoring two crucial market dynamics.
First, the distinction between strong hands and weak hands. Accumulation phases like 2015-2016 and likely 2019-2020 are defined by weak hands (people selling for a loss or small gain out of fear) selling to strong hands (those who intend to hold long term, no matter what). That's actually why accumulation phases form. Strong hands buy up all the supply in the range, and when there is no supply left, the price gets marked up.
Second, the distinction between fear and greed, which is a related concept. In the early goings of a new bull market, the market is usually quite fearful, still reeling from a previous bear market or range trading dynamic. That means traders are skeptical of any bull market and are likely to sell quickly instead of holding for long term gains. That's the type of sentiment we saw in late 2015 and early 2016, and it's why 2016 was a slow grind upwards rather than a parabolic run like 2017. In a bubble, that sentiment changes dramatically. Fear gives way to greed, and everyone becomes scared to sell because of FOMO.
That's the difference between 2015 and 2017. In 2015, everyone was fearful and wanted to sell. In 2017, everyone was greedy and refused to sell. And that's how we went ~130x from low to high.
What is 130x from (the 2018) low? It's in the $400,000s.