I have often asked this question as well....
I have a lvl 45 Carpenter (my main adv char) & a lvl 70 Provisioner (only lvl 19 adventure)
On the carp I can do rush orders all day long and just pump pristine stuff out like mad, however, the provisioner can't do rush orders & has to pound the durability keys like mad (& still fails regularly) to the point of having to wait for mana regen in between attempts. Extremely frustrating! She has even failed with the Provisioner's insight buff active.
As you can see I toughed it out, but, OMG was it agonizing & frustrating!!
Everyone I have talked to about it just says "It's just luck of the draw"