Possibly liability issues?
They make the service manual open. Someone opens the battery and fries themselves, and then their next of Kin sues Zero?
But then they opened the battery against either "don't open the battery" or "don't short these contacts" warnings in the manual, and Zero can say "we told you so. you ignored our warnings.". I'd think that exonerates Zero more than anything.
Just like with my ICE bikes. I've read the service manual for my FJR & SV and know which areas of the ABS are "strictly do not f**k with" and I know how to safely change the fluid, test the HU, or replace the brake lines w/o compromising my anti-lock system.
I've NEVER been able to get hold of a service manual legitimately, not for any Kawasaki, Honda or Suzuki I've owned, on the few occasions I've asked the manufactorer (or dealer) I been polietly told to **** off, dealers have that sort of thing wrapped up.
Yeah, I used to have the same problem, but now I simply insist on buying the manual and don't take any shit about it. I buy all my stuff online nowadays from ronayers.com and other places because the local parts-monkeys are morons.
I've never owned a Kawasaki, but I've got factory manuals for my Yamahas, Suzukis, and Hondas. They're expensive though, usually about $150 or so.
Hell, Ron Ayers even sold me the Suzuki dealer diagnostic system (a USB box for the bike and some Windows software) which I needed to test the ABS pump and sync the throttle bodies. On 2008 and later Suzukis, they have an air equalizing valve between the throttle bodies, and you need a laptop to disable it so you can sync them. That was $700.
On my FJR, I insert a jumper, do a dance with the kill switch & starter button, and I can test the ABS. No laptop necessary.