When you want to get rid of a weed problem in your garden, you pull up the roots. If you don’t get the roots and just hack at the growth from those roots, the weeds will grow back.
This is the same for labeling GMOs. Labeling does not strike at the root, but addresses the problem after the fact. After the plants have already grown, multiplied, and contaminated everything around them.
Banning is striking at the root. If they are not grown, they will not multiply and contaminate.