MSO is closed, proprietary, whatever, but it's actually a fine piece of software especially compared to OO and LO. Word, PowerPoint and Excel are so good that people end up overusing them for stuff they're not intended to. Others like OneNote or Visio are extremely useful, too. They might not be the best on each category, but together it's a very powerful suite.

Plus, MSO is multiplatoform on Windows, Mac, iOS and Android. I'm unaware of mobile versions of OO or LO.

Everyone I know, including myself, that uses OO or LO is because it's free (as in freedom for some, as in beer for others) and can read/write MSO files to an extent.