Correct me if I'm wrong, but isn't forcing you to divulge your encryption password compelled speech? So the police can crack my phone but they can't force me to tell them my PIN.

Yes, you cannot be compelled to testify against yourself, but Microsoft is under no such obligation when served a warrant because of third party doctrine. Microsoft holding bitlocker recovery keys is considered you voluntarily giving the information to a third party, so the warrant isn't compelling you to do anything, so not a rights violation.

But, the 5th amendment is also why its important to not rely on biometrics. Generally (there are some gray areas) in the US you cannot be compelled to give up your password, but biometrics are viewed as physical evidence and not protected by the 5th.

Warrants are a mechanism by which speech is legally compelled.

The 5th Amendment gives you the right to refuse speech that might implicate you in a crime. It doesn’t protect Microsoft from being compelled to provide information that may implicate one of its customers in a crime.

In theory...

In practice: https://en.wikipedia.org/wiki/In_re_Boucher

The government gets what the government wants.

They can't force you to tell them your PIN in some countries, but they can try all PINs, and they can search your desk drawer to find the post-it where you wrote your PIN.

In the UK they can jail you just for not providing an encryption key

In the US.

But this is irrelevant to the argument made above, right?