As a matter of fact, the low branches' growth is suppressed by the apical dominance of the upper branches, which contain more auxin and grow more vigorously.
I've worked extensively with cuttings from both upper and lower growth and find that low growth is slow to root and VERY slow to 'take off' after doing so.
The reason you use a rooting hormone like dip-n-grow is to make up for the low concentration of naturally occurring rooting hormone in the more desirable upper branches.
Also the low branches tend to have a woodier, almost bark-like covereing, that new roots can't penetrate without the grower scraping it off.