If the Rose Bomb is so powerful and poisonous, why didn't the hunter association airdrop a dozen on the palace when fighting against the ants? In Hunter x Hunter, why didn't the hunter association airdrop a dozen of Rose Bomb on the palace and called it a day when fighting against the ants?
The could have used the teleportation guy to drop a couple dozen of those roses and boom, they're all dead. And even if they're not, there's poison to finish them off. That would've been so much easier than fighting them.
Also, it's not farfetched to assume that the hunter association has a special distress signal to contact Ging. Call Ging. He snaps his fingers and bam, all the ants drop dead.
Netero wanted to settle the matter as a Hunter first, but implanted the bomb within himself as a contingency plan. He went in personally and fought Meruem. He lured Meruem away and fought him solo in the desert, when it was clear that he could not win, he killed himself, triggering the bomb a safe distance away from any casualties.

Also, HxH is a shounen series and they had to settle it the shounen way, with a 1v1 fight.