Because you get all of the problems that you get mentioned in the article. And on top of that javascript land is fad heavy, and whats cool today might not be cool 2 years from now.
I personally know of a story where a startup started with datomic and clojure, and it was a bad idea because datomic could not effectively delete things. Eventually they went the standard java and standard cassandra / postgres / redis type route.
He was working in a health startup and this was something like a couple of years ago. He said that datomic was immutable so actually deleting things to HIPPA standards was not possible I think. They might of fixed it by now.
Having installed a medical records system for live-fire use by an optometry practice, I can say that it's exceedingly rare that you ever want to delete anything that is logged in a medical records environment. It's so rare that it's never been done on the four or so years I've been maintaining the system.
You're correct that Datomic considers immutability a feature. That said, Datomic on-prem supports excision which completely removes data for exceptional cases. I suspect Datomic Cloud will sometime in the future.
With EU's GDPR (General Data Protection Regulation) looming on the horizon I think Cognitect would do themselves a disservice should they not include excision in their Datomic Cloud platform sooner rather than later.
