Two possible reasons i think of -

1. DDOS attack on the website ( bitconnect.co ) and rest of the exchanges have synced up with the website price , as soon as website was shutdown there is no way that price is maintained on exchanges any longer.

2. Arbitrage trading buying for cheaper prices on exchanges and dumping it on bitconnect website for huge profits , flooding the website which prolly makes sense for website to shutdown transfers and loans.