If Zcash had privacy by default, they would have won against Monero for being the private cryptocurrency. As it stands, any private transaction on the Zcash chain stands out like a sore thumb and the use of de-anonymized transactions around it make it easy to figure out how much money was moved. It was a missed layer 8 opportunity on the part of Zcash.

This attack doesn't seem to work if you run a monero node, though.