Not to criticize, but reverse engineering is not a perfect science. It is of public notoriety that Microsoft uses closed format (even when flagged as open like OOXML, which is even not truly implemented by MS itself) to ensure the lock-in of its user base. You can find good literature about open standards, open formats and the likes on the internet. You can also note that Microsoft is a board member of the OASIS, the foundation that defines the formats used in LibreOffice and OpenOffice. For instance, this quote from Microsoft :
“As an OASIS Foundational Sponsor, Microsoft is pleased to see the approval of ODF 1.2, which Microsoft participated in and supported. This is an important milestone for the ODF format and the ODF community.”
– Doug Mahugh, Senior Standards Professional, Microsoft
So, a better question would be : why the ODFs are so poorly supported in MS Office? Why can’t it provide a good conversion tool from pseudo-OOXML to ODF?
What’s more, TDF (the foundation behind LibreOffice) members are spending a lot of time (and money) improving the OOXML filters that could be used for functionality or usability enhancements. For instance, German and Swiss public administrations are spending money on this, that is, to do the job MS should do.
So yes, there is an interoperability problem between Excel and Calc, but the guilty is the one who closes the gates to prevent its people from leaving. Strange vision of “free market” and “free and undistorted competition” isn’t it?