Simple:
The difficulty tanked 📉.
It's estimated that ~90% of XDN Miners were merge mining Monero XMR with DigitalNotes XDN. After the fork these miners were left with no choice but to drop XDN or continue to merge mine it with Monero 0 XMO... as expected DigitalNotes difficulty fell to all-time lows.
You can mine 6x the XDN as a couple weeks ago and the price has risen 40% since.
It may not be the best coin to mine, but if your confused with the numerous Monero's that cropped up and like the cryptonote algorithm; it's a viable option.
The developers will likely switch to PoW7 soon. Until then this coin is alive with a handful of miners... including me.
DigitalNotes XDN can be mined with your favorite cmd miner or a GUI/Pool miner like Minergate:
https://minergate.com/a/7fb471ecc9fc984387f17bb5