Earlier quoted context omitted.
Because if you make it too easy for the police they'll just ask for too much all the time, even for things where they wouldn't get a warrant. This is happening in Germany all the time when a provider wants to be nice to the police. If they say "we'll get a warrant anyway", just response "okay, so get the warrant and come back and I'll give you the data". Then at least it's up to a judge to decide where giving out dat…
See my edit. I'm assuming they can verify the allegations, due to the nature of BTC transactions. A warrant possibly means that they go out of business, because the servers are physically seized. If you tell me you'd risk that for a stranger who you can tell probably committed a crime, I don't believe you.
That's a very very slippery slope. It is the job of the police to not look into data not related with the case, not yours.
Surrendering the info would be giving the police more power if anything since, they now can come and get data from anyone without a warrant (how do you even know that this account is dealing drugs other that "the police came looking for him"?).