I wondered that too. But after some thought I think it is other stuff. The unit is ready as it will ever be. Software will continue to improve and they have to draw the line somewhere.
I think any delays now are more to do with the next phase of tuning their business, e.g. post production. Things like logistics, improving yield quality, business agreements, modules, website, sales, customer care network, repair centers and the thousand other challenges that go with operating an international business.
This HMD will have vastly more demand than their 4K unit.