It's also not nearly as scriptable as Word is. Word has had macros ("fields") since its first Windows versions, VBA for over 20 years now, it's easy to develop complex add-ons - where I live we've had one for grammar checking for decades now (speaking of that, Google Docs' language features for less popular languages are far behind Word's). Various software supports export to Word and some programs even import from it. You'd be surprised what levels of automation has been achieved with Word.

Files are also easily shared (on physical media, email, no need for anyone to have a Google account to edit and send them back), encrypted, burned onto a CD for storage. DOC/DOCX are ubiquitous and stable file formats. No worries about data leaks in the cloud as it's all local by default...