There is no real alternative for MS Office currently available, that is true. Whether that is because Office is good software, or just de facto, is a different question.
But businesses also tend to stick with the platform they have, not necessarily because it's the 'best' (whatever that means), but because they have invested in it. They don't want to throw away that investment and invest even more to another platform. The larger the company, the more reluctant they are to switch away from their current platform.
If a company has spent hundreds of thousands, or even millions of dollars to develop and maintain an ERP, an accounting or helpdesk system, etc, etc, whatever it is they need to run their business, they are not going to switch platforms. And it's not just software they need to think about, but hardware too. Switching to another platform might render a lot of their hardware useless. You'd be surprised how specific the hardware needs of some companies are, and how specific the software needed to run that hardware is.
Heck, businesses are't even going to upgrade, unless they are forced to. Just look at the share of Windows XP. It's twelve years old, and running out of support, but it still has 33,66% market share. Windows 3.11 support ended last year. Yeah, it really was an officially supported Windows version a year ago, believe or not. There are still countless POS systems, CNC machines, crimping starions, inventory systems, etc. that use it, and they won't be upgraded, because the hardware does not allow that.
(Edit: Add the cost and trouble of training users to a new system to all of the above.)
Businesses are stuck with what they once chose, and usually that is Windows.