Good point. Wondered the same thing. My guess is that the file format for Live projects is easier to handle. And/or it’s a licensing deal. There are several iOS apps which support it and they all give you a free license to Live Lite. Bitwig hasn’t done much of that, apart from bundling 8-Track with a few pieces of hardware (including some ROLI ones). Could be cool if Bitwig were to import Live projects.
What would be great is if ROLI (through JUCE?) could ease out the coming of some project interchange format. DAWs have all sorts of quirks but their project files are probably very similar. In terms of compatibility, it a ounds like music software is at the point where productivity software was in the 1990s. You can open Excel files in LibreOffice but you can’t open Live files in Ardour.