It was the most profitable year because it was so easy to gain a thousand percent profit with almost every ICO or altcoin. Now, there are profits, but it is really hard to predict which coin will explode to the moon. Currently, we no longer see such increases on DeFi coins.
Don't forget that, during the 2017 in the eyes of ICO things where good because of their new invention compared to this 2020 with the event of Defi, this two event has actually helped in the beginning to a new era in the cryptocurrency industry. What happened in 2017 has taught us a big lesson that we won't take this 2020. The hype of 2017 did more harm than we thought and investors are just be careful with the 2020 hypes.
Therefore, 2017 is hardly a golden year for cryptocurrency. Most likely, it can be considered a year of great opportunities for participants in the cryptocurrency market.
The rise in prices for cryptocurrency in 2017, and first of all for bitcoin, was too fast and therefore it was followed by the same rapid and deep fall, and this also led to the onset of the mevezhy market for the next two years.
I don't know if this can happen again in the future, but the cryptocurrency market was not prepared for such growth then.