MAXQ
I think part of this is also reducing the stresses caused by the MaxQ.
A lot of engineering goes into stopping a rocket being crushed between the dense low altitude air and its own motors.
By starting the launch at altitude the air is ruffly a 5th as dense hugely reducing vibration and friction allowing for a simpler lighter rocket to do the same job.
At the moment they are limited by having to work with off the shelf gear not really designed for their application, with any luck this will get resolved and thy will be able to make a run of this.
PS not a rocket scientist if i have goofed this please tell me i am a Muppet ;->