What’s the point of wannacry for exchanging bitcoins to monero?

At first glance, exchanging Bitcoin to Monero makes sense.
But why using Monero with an exchange which is likely to help the police ?

I mean Monero transactions are private only on the block explorer : the sender has a key (view key) which allows to view to who and how much was sent…

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