what s the reason of this big decrease?
Just hang in there, this is still early for this coin and we need more people to find out about it. The new airdrop scheme is going to bring new people and they will be more interested in holding to increase their coin. I think it will bounce back and go up nicely in the coming weeks.
Probably the SegWit adoption in Bitcoin itself.

Yea, I am just wondering myself, what is the advantage of this coin when Bitcoin/Litecoin adopt SegWit with larger blocksizes? Are there features in the pipeline that make Bitcore unique/better than those? I can see that in April Bitcore made lots of sense, but what will happen after August?