This is all a bait for BB to kill Garp, then Kuzan saves his teacher and ends up dying instead.
Dead Garp aint worth anything to BBPs.
He may be a better bargaining chip for blackmailing WG.
Other than that, I dont see a point why they would off him.
He has no Devil Fruit to be gained from killing him.
But if Kuzan steps in, it might lead to his eventual death.
That way, going after Garp has some purpose, kinda.
You're acting like Oda has never created plot points that lead nowhere lmao. That's just a usual day in his office.
Now that you mention it...