Because people keep secrets on computers. You cave the combination of a tiny percentage of people who have secrets that are life threatening, and millions of people use bitlocker because its built into Windows. Its a tiny number times a huge number.

If I had to guess, that might include journalists who investigate authoritarian regimes, activists who keep their identity secret, and minorities who live in countries where their identity is a capital crime.

Then there are probably also governments who rely on bitlocker to secure the computers of people with state secrets like the identities of spies. Probably lots of other weird edge cases.