Zerocash is much better and upgraded version of zerocoin and why does PIVX implement an older version of algorithm.
"Zerocash improves on an earlier protocol, Zerocoin, developed by some of the same authors, both in functionality (Zerocoin only hides a payment's origin, but not its destination or amount) and in efficiency (Zerocash transactions are less than 1KB and take less than 6ms to verify)."
Zerocash is not trustless, it realize on somebody keeping the network private. That person or persons can also create coins out of nowhere without anybody knowing any better.
Thanks for your response, could you please elaborate on this.