A # of reasons why...
Deadly Ernest, I've never used Libre Office, but you could be right in terms of use of the software as an individual. However, from an enterprise perspective, an organization has a number of financial and operational concerns that goes well beyond individual use. For instance, mobility and co-authoring of documents are big ones. Many of today's enterprises need to be able to reference a document from anywhere, without having to be concerned with moving a file manually in and out of a document share. Financially, a SaaS-based office suite makes a lot of sense, because licensing and support costs are drastically cut, as well as the cost to administrate. Lastly, just because you have software on a PC doesn't mean it is secure. In fact, I'd go as far to say that on average, on-demand services offered by Google and Microsoft are just as if not more secure that a well protected machine. You should read Google Apps' and Office 365's SLA. You'll be surprised at what you find.
