Because investors who bought NEO before airdrop is dumping their coins now because they already get the ONT in their wallets just like happened on Ignis airdrop that when you buy Nxt you will receive 0.5 Ignis on every 1 Nxt and after that within just a half an hour the Nxt dumped so hard, But no need to worry Neo is a good coin just hold it and wait for another good pump.