Because it's not 100% compatible with existing VBA macros.
The value to businesses isn't in the ability to program things. The value is the ability to continue running something that some previous employee wrote a decade ago that seems to at least mostly work, which noone currently employed understands (hell, even the author probably doesn't know what it did anymore), and they don't want to touch those processes at all let alone port or rebuild them in OpenOffice macros, even if some of the stuff is semi-compatible.