It seems DGTX have some pump in dump in their previous announcement. Price surge when they release an update then slowly the token were pumped. And to answer OP's question, it is simple, after the pump and hype rally, someone dumped the coins to unsuspecting buyers probably an exit to take profit after the hard labor of hyping the token.
What happened with the project?? Is it still safe to purchase this coin??
If you can risk your investment then you can purchase it. But if it is me, I would dig more information about the dump and see if the dev has something to do with it.