There are so many integrations built on top of the Microsoft stack. Many users I know have 3-4 additional toolbars in Outlook and Excel that handle all sorts of different tasks. Some in excel will pull data automatically from the accounting system and massage the data to generate the report with a click of the button from a user. In outlook there are integrations with salesforce, CRM, and document management systems.
There are also a myriad of macro enabled spreadsheets that are constantly being updated and have been working just fine for a company for years. They are not going to take the time to try out a new office suite to see if they can save a relatively small sum of money. Most editions of MS Office for a user cost less than what they pay that typical office worker in a single 8 hour day.
I know Libre Office has made strides to be more compatible with the MS file formats, which is great. However, they will not be able to make much market penetration until they can offer 100% compatibility with all features of MS office. At the end of the day, people want things that just work. They have no ideology about free or open source software and most don't have any hatred towards Microsoft.