I see no evidence to support the statement "Bitcoin is mainly used in drug trading these days."

I do see some mild counter-evidence. There were two very large dark-net markets that were shut down recently, and the price of Bitcoin didn't seem to respond.

That's probably because most people see drug markets as a completely replaceable service. Silk Road down? Use AlphaBay. AlphaBay down? Use something else. It's so profitable to run these markets that the odds of someone developing a newer, better version are guaranteed.