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.
Not solely, but since sooooo many documents are already only available in PDF, you need to support it for backwards compat alone, plus all the people who just wouldn’t migrate their data to a new format because the old one still works for them.
I’d love if there were a true open standard with the same capabilities and support, but you’re not gonna get companies to adopt that out of the kindness of their hearts.