Bottom for BTC seems to be around $100 billion market cap based on technical analysis. Also I don't believe it was retail investors who brought the price to $20,000. I think it was hedgefunds. Retail investor came later on after the price was over $10,000 from what I can see and yes they contributed but hedgefunds seemed to be behind the majority of it.

There could be an exception to this too. In 2017 Asia played a big role. South Korea in particular was where most of the retail activity you are talking about seemed to come from. But in the United States I don't think it ever reached the mainstream level. People only started talking about it when it was near $20,000 from what I remember.