Big Tech Companies enjoy a weird kind of megalomania, when viewed from outside. The net-effect of their announcements usually are: "We will tell you soon how we plan to announce our universe-changing plan to make everything work the way we think it should. When we figure it out we will announce how we will announce our plan. You will be even more impressed then than you are now."  

It is thus because in the meetings leading up to the big day, they can only agree that they will make an announcement, not what it will be. That comes later.  

In the meantime the partners have some demos. They don't do anything other than show how, when the BigTechCo's finally figure out how to announce their plann, they will submit to their will and become rich and powerful in their own domain. 

What really matters are the TechCo's, large and small, that are not on stage. That usually is the point of the whole mess. "We invited them," they will say, "but they wouldn't come to be part of our open announcement of how we will announce our plan to dominate everything and do things the way we think they should be done (when we figure it out)."