[Robotbeat]

For the same reason that just because you can balance on a balance beam 30cm from the ground, you'd probably be hesitant balancing on one 5 meters off the ground.

EDIT: If you want to see him testing the concept in a bunch of iterations, you can check out the vimeo page here: https://vimeo.com/gravityindustries/videos/

Arguably, the leg-mounted jets COULD be close enough for ground effect, but they're apparently destabilizing so they switched to two backpack-mounted engines instead.

[SideburnsOfDoom]

> just because you can balance on a balance beam 30cm from the ground, you'd probably be hesitant balancing on one 5 meters off the ground

I get what you're saying, but when applied to someone supposedly building flying machines, I just find it a bit of a thin rationale.