Why do home-made pickles float in the jar, but commercial pickles don't?
Most likely commercial pickles are preserved by an accurate pasteurisation and ascorbic acid or other chemical preservatives so that the "brine" contains much less salt as compared to your homemade ones.  It is mattert of the liquid density, yours is heavier.

(Though the density of the vegetables might likely vary a bit - and though surface/volume ratio could have an effect on how much water flow throughout the skin of the preserved vegetables - I would expect it to tend to the same value upon preparation and storage).