I love immutability and Datomic as much as the next Clojure programmer. But this sounds quite a lot like post-hoc reasoning.

For example, there's quite a few situations where you require mutability in bank data (e.g. with government requirements, or when you want to rollback fraudulent trading). Sure, both are solvable with Datomic, but they don't scream "huge advantage with an immutable datastore".

And there are plenty of highly competitive industries where code quality matters, but they're not flocking to functional programming.

Don't get me wrong, I think functional programming is an absolutely great way to structure and think about programming (and have coded professionally in Clojure for the last 5 years or so). But I suspect the prevalence of FP in some industries is as much chance/social reasons than it is for some inherit superiority in the approach.