Speaking of Orochimaru alone.
To be fair, though.
How could dealing with Orochimaru be easy?
In terms of raw strength.
Orochimaru certainly could not compare to Madara Uchiha.
Uchiha Minamoto could crush Madara Uchiha with ease, and could crush Orochimaru just as easily.
But speaking strictly of survival.
If Orochimaru claimed second place in the Shinobi World for his means of staying alive, no one would dare claim first.
Uchiha Minamoto knew very well how troublesome Orochimaru was.
Even if he went to the Land of Swamps shortly and disposed of Orochimaru cleanly and efficiently.
That still would not guarantee that he had truly killed Orochimaru.
Who knew how many "backups" that sinister, vicious snake had scattered throughout the Shinobi World?
Orochimaru possessed "cloud backup technology" unique to him in the Shinobi World.
Every person Orochimaru had marked with a special Cursed Seal could potentially become his "backup vessel."
Orochimaru's current subordinates, such as Kimimaro; his former subordinates, such as Mitaraishi Anko; and perhaps even other unknown targets...
It really was a case of "kill one Orochimaru, and countless more Orochimarus remain."
Furthermore.
Sealing Jutsu was also meaningless against Orochimaru.
Just look.
In the normal timeline.
Orochimaru had revived through the [Cursed Seal of Heaven] branded onto Sasuke Uchiha, only to be instantly sealed by Uchiha Itachi using the legendary [Totsuka Blade].
But so what?
Had Orochimaru not later revived again through the "backup Cursed Seal" on Mitaraishi Anko?
Uchiha Itachi, who supposedly had endless trump cards and could pull a deus ex machina out of nowhere at any time, had practically torn through his crotch digging before finally producing a [Totsuka Blade] to seal Orochimaru.
Yet even that could not put an end to this venomous snake!
Therefore.
Uchiha Minamoto had never entertained the idea of completely exterminating Orochimaru.