Why is the Rasengan in this series?! Why is Hyouton in this series?! Why is Scorch Release in this series?!
Because its something Kishi invented and put into the story.
The Byakugan allows for one to most efficiently use Jyuken. By being able to perfectly see the Chakra network, one can simply inject his or her own chakra to damage vital organs and halt another's use of chakra. It also allows one to more efficiently use their chakra as being able to see things like Tenketsu allows one to fire chakra from it creating shields like Rotation, or directional attacks on ridiculous scales like Hiashi's Air Wall Palm.
Additionally, the Byakugan has near 360 degree vision, telescopic vision of up to 10K (at least by Hinata), X-Ray vision, skilled spatial reasoning (dodging the Mokuton spikes and deflecting specific ones endangering others), and seemingly high speed movement tracking (at least for Neji who like Kakashi used his Dojutsu when Lee started moving in Gates).
Its not an eye that grants OP powers like the Sharingan and Rinnegan. Its an eye that lets one better observe things around them, and ultimately use chakra more efficiently.
