The Foundation sees this as a contradiction to the EU’s own interoperability goals. Although XLSX is standardized as OOXML according to ISO/IEC 29500, Microsoft’s implementations often deviate from the specifications. Furthermore, features often change undocumented, which complicates compatibility with open-source software such as LibreOffice.
…and bribed the represenatives of the “new” IETF members as well as their governments to vote for Microsoft’s standard. The latter was, of course, a matter strictly between “business partners” and probably barred behind NDAs, so “legal” as long as nobody would blow the wistle.