At first glance, exchanging Bitcoin for Monero makes sense. But why use Monero with an exchange, which is likely to help the police? (And which did.)

Monero transactions are private only on the block explorer. The sender has a key (view key) that allows one to view to whom and how much was sent.

So, what’s the point of using Monero in that case, rather than something that would resist investigators, like Zcash ?