Extending ODF was not possible because Sun would not allow it. Sun's IP licenses for ODF effectively gave them veto power over attempts to add things to ODF that they did not approve, so that was the end of that. Sun's position was that ODF would support exactly the feature set needed by StarOffice.
If you ignore IBM's and Sun's massive FUD campaigns against OOXML, and actually compare the specs, you'll find that OOXML is not anywhere near as bad as they claimed, and in many ways is better than ODF. ODF does have nicer markup--I'd much rather read or write by hand an ODF file. On the other hand, ODF is incomplete in major areas, and other areas are imprecise. (Sun and IBM actually tried to use this as a point in their FUD campaign, slamming OOXML for having too much detail).
It's seems likely that Sun's IP licence was specifically written to stop Microsoft from doing its well documented embrace, extend, extinguish routine on ODF like they did to Sun's Java. Instead they just emrbraced, extended and extinguished the entire idea of a standard XML office format. Nice work.
Weirdly, Microsoft seem to have incompatibly forked their own OOXML format and are in no rush to fix that now that they've seen off the competitive threat posed by ISO standardisation of a competing format.
StarOffice and Microsoft started work on XML formats at around the same time, and most of the subsequent histories are largely parallel. There was no EEE here.
If you ignore IBM's and Sun's massive FUD campaigns against OOXML, and actually compare the specs, you'll find that OOXML is not anywhere near as bad as they claimed, and in many ways is better than ODF. ODF does have nicer markup--I'd much rather read or write by hand an ODF file. On the other hand, ODF is incomplete in major areas, and other areas are imprecise. (Sun and IBM actually tried to use this as a point in their FUD campaign, slamming OOXML for having too much detail).