Does every plane go through this where they have to go through like a year of jumping up for 5 seconds then landing again before they fly commercially, or is it just because of the sheer size that the 787 can't get off the ground and fly around for an hour.
All new aircraft want to be tested in incremental steps to ensure that everything is working as designed.
If there is a problem with the controls or landing gear, it is safer to be just off the ground at rotation speed than coming from 20K feet up and landing at speed.
And if you paid attention to the flight, it did fly for a hour or so.
Boeing will have about a half dozen flying almost around the clock now doing test and equipment evaluation.
Chief pilots from major customers will be getting rides then checkouts also.