This is one that Andrea and I have discussed in person and my take on it is just that there are some people who just don't get the maximum benefit due to their lack of an electrologist fast enough to catch the hair growth phase and keep at it long enough to get to full permanent clearance. (let's face it, there is a big difference between someone working at 100 hairs per hour and 500 hairs per hour, or even 1200 hairs per hour)
To be fair, there are also the people who don't see their electrologist near long enough, or frequent enough to get anywhere at all near full permanent clearance.
The only people I have ever had trouble clearing are the ones who don't come on schedule, and the ones who refuse to stop plucking. I even have a plucking former client who is happily paying a slower electrologist more money than I charge for less work, because she thinks this other person has "a better kill ratio" than me. Little does she know or believe, that our problem was simply that she never stopped plucking, so I never got to kill off the hairs she plucked every day.