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.
Let me assure you that the original board that was voting for Open Office’s proposal was absolutely pissed off, short of dissolving but eventually unable to revert the decision because of it’s formal correctness.