Market cap was that high back then because the spot value of coins was also so high. While it is true that the volume was larger back then, the numbers presented in charts and statistics were partly calculated using the spot value of crypto meaning it magnified total market cap and presented an illusion which seems like there was tremendous support.

Don't worry tho because we are on the way back up. I speculate that by the end of 2018 we should be right back to those numbers.