In general, because of the superior insight of the byakugan, it can glean more information from a LONG and practically undetectable distance, which is also useful for not just the person alone, but possibly the entire village when it comes to espionage and infiltration missions.
You can also use the byakugan as a long range sensory as displayed by Ao to detect enemy forces from a distance, allowing the village some time to prepare a counterattack.
If someone where to obtain a sharingan, then in a 1 vs 1 they usually had an advantage over their enemy, but outside of that, there is very little use for it since its sensory ability is limited to only seeing chakra flow and color and only in direction the person is facing.
Also, there were plenty of uchiha who couldn't awaken the sharingan, so it wasn't alwas available for someone to take, where as whenever someone did face a proficient sharingan user, it was highly likely that the person they fought against would lose if they fought alone, minimizing any chance of obtaining the sharingan for themselves.
One last thing to note is that whole the byakugan can be activated and deactivated after being transplanted, the sharingan cant be deactivated once transplanted, causing significant chakra draining to anyone who isn't of uchiha bloodline.
Overall, if someone just wanted power for themselves no matter the cost, then the sharingan is the way to go. If they wanted to help not just themselves but their village too, then they would go after the byakugan.
