I remember when Microsoft first attempted to prevent the standardisation of Open Document Format (used by LibreOffice and others) and then bullied its way into getting approval for own OOXML standard. Already back then, supporters of FOSS warned that Microsoft would use the overly complicated OOXML to maintain its stranglehold on users of Office-like software.:

Whenever applicable and possible, standards should build upon previous standardisation efforts and not depend on proprietary, vendor-specific technologies. Albeit, MS-OOXML neglects various standards and uses its own vendor-specific formats instead. This puts a substantial burden on all vendors to fully implement MS-OOXML. It seems questionable how any third party could ever implement them equally well, especially when a standard comes with 6000 pages of specifications without serving its minimalistic purpose.