Because, of course, it's natual to open an email from a company you have:
a) never heard of
b) have never dealt with
c) have no intentions of dealing with
d) that you aren't expecting
I'm guessing your policy is to basically open anything and everything, regardless of if it contains a virus or not - as that's what you have just implied.
Yeah. I know it's weird but sometimes, in some businesess, you have these funny things called customers, and sometimes customers contact you out of the blue because you've not yet dealt with them before.
And sometimes these customers who you've never heard of before send you quotes from other firms to invite you to compete.
A lot of businesses, quite strangely, rely on customers to remain in business. And if you cannot meet your customers needs, they go elsewhere and you go under.
I guess your business never grows eh?
How do you hire staff without checking their CV? Those are usually some form of document.
And then there's the firms and government depts where staff handle hundreds of documents every day. Companies sending in spreadsheets to tax firms/accountants/IRD etc, clients sending in CVs/quotes (car repairs, medical, stuff for clothing for job interviews etc) to welfare agencies, invoices for work done (verify that the work has been done of course) - the person who opens the incoming invoice may never had heard of the firm claiming the payment - some businesses are a bit larger than mom and pop who only deal with the corner grocery store y'know.
Some firms need to be able to open documents that come from people they've not heard of, otherwise they don't get new customers and without new customers they quickly go broke. So, what is needed instead of a (sometimes) silly "don't open all these documents under these myriad conditions which won't catch everything (see Wannacry for a start, plus Iloveyou etc etc etc - all from people they knew and trusted) is a robust system for receiving said files safely.
That means a well-cared for system with decent AV scanning the incoming emails at the server level, so nothing can get through. If LO etc are incompatible with MS's "infect on open" macro, then use them at least to preview a copy of the document (if they have the same or similar flaws you're going to have to rely on incoming scanning), stripping macros (if it can still be done automatically without opening in Word etc), and of course having the receiving machine get lots of backups and able to be killed and restored in a moments notice (like a VM).
Of course we had it easy. We could safely open any document we wanted to without fear of malware, because we did run email scanning at our end as well as decent spam protection, and any documents we opened were opened by the secretary in Libre Office on her Linux machine. On the off chance that any one tried to send malware it would've simply been unable to work at that stage.