Just say "we are storing your keys on our servers so you won't lose them" and follow that with either "do you trust us" or even "we will share this key with law enforcement if compelled". Would be fine. Let people make these decisions.

Besides, bit ocker keys are really quite hard to lose.

is it just me or would "Microsoft refuses to comply with a legal search warrant" be an actual, surprising news story? like of course MSFT is going to hand over to authorities whatever they ask for if there's a warrant, imagine if they didn't (hint: not good for business. their customers are governments and large institutions, a reputation for "going rogue" would damage their brand quite a bit)