Jakson is really into Legos. He loves to build his own robot creations, cars, and flying contraptions. He's been begging Zak to help him create a BIG bridge for awhile. Jakson is convinced that since Zak "builds roads" as a living, he must also know how to build bridges.
Honestly, I think the real motivation behind building a bridge is that Jak wants to be featured in the Lego magazine he gets every month. It's all about the fame.