All these are effects, not causes.
The real cause:
This shitcoin was distributed for free to Bitcoin holders, and further airdropped to registered Bitcore holders. Increasing selling pressure in the absence of a use-driven demand.
Byteball and Bitcore are siblings - bottomless shitcoins with interesting technology ideas and absolutely no reason for holding.

PoW mining does not make Bitcore any more valuable - the share of mining reward to existing supply is very low, rational miners don't hold coins below their average cost of mining - they dump them.

Yeah, I am salty about the price...