Amberser was a man who never forgot his initial purpose, no matter where he was or what he was doing, his ultimate goal was always to make more money.
Since the Orcs and the Laine had started fighting, such an important event was too good an opportunity to make money to miss.
Last time when the Laine waged war on the Orcs, Amberser was busy handling the Deity Position of the Rose Spider Queen. This bigger business was more important than profiting from war, which is why he missed that chance.
By the time Amberser had a moment to spare, the Orcs had already been defeated by the Laine.
Now the timing was perfect, as the Orcs had won back some ground, returning both sides to a state of evenly matched strength, creating a market for Amberser's Undead Troop.