The Pokemon you get here is randomly picked I believe when you get your starter, or maybe its talk to Victoria. The same holds true for the mystery egg, Espurr/Minncino, Joltik/Grubbin, etc.
But...Zigzagoon's not useless. Its more useful than Pachirisu really, not that that's hard. It gets Pickup (which admittedly Pachirisu does as well), gains Mud Sport by level up, allowing you to totally negate Julia's field, learns pin missile by level up, which devastates Florinia's team, learns most of the HM moves, etc. Not to mention getting headbutt, a 70 bp STAB move really early. Its a solid Pokemon in the early game.