The TaiFu™ 30 Index is a market capitalization weighted index of the largest 30 cryptocurrencies for that day. Each day, a new top 30 is selected to calculate the index. It represents the largest 30 cryptocurrencies on a given day.
Based on this it can be seen that the top 30 cryptos fell in the past few days.
In my opinion the reason for the sudden crash is due to whales pulling out of the cryptocurrency market due to uncertainty surrounding the 1 August soft fork that is going to occur.
This article from bitcoin magazine indicates important dates for the implementation of the fork
https://bitcoinmagazine.com/articles/countdown-segwit-these-are-dates-keep-eye/
Based on this I think that on the 14th of July it'll more clear as to whether the market continues to fall or turns around. Uncertainty should arise again on 1 August.
Please comment if you've identified other reasons for the sudden crash.