cryptocurrencies being liquidated to cover tax bills.

There is an excess of ethnocentrism here.
The correct sentence is:

"cryptocurrencies being liquidated to cover USA tax bills."

This would potentially account for a large amount of the recent price drop

From 1st April 2017 to 18th April 2017 bitcoin price rised from 1100$ to 1250$...
It's a +12% gain

In 2017, USD was among the most traded currencies traded for bitcoin, behind the Chinese Yuan.
In 2018, USD still is among the most traded currencies traded for bitcoin, behind the Japanese Yen.

The American dollar is as much traded for bitcoin than it was in 2017.
In 2017, tax day in USA didn't affect Bitcoin price
In 2018 many American traders thinks their tax day influences Bitcoin's market.

I'll let yourself make your own conclusions