Their reason for manufacturing a Golem was simple. When they thought about how they were going to take down Metafel after the general had evolved into a level 8 Eater, they naturally came to the conclusion that they needed to create something so strong that even the evolved Metafel wouldn't be able to beat it. When it came down to it, their only option was to use the core.

Although the core was defective and could only discharge energy for a few minutes, it didn't change the fact that it was a level 8 item.

"Are you really done analyzing it? Can we really make a Golem out of it?"

[I have found out everything I could. You should be able to create a Golem, Master.]

"...Alright, let's bet it all on the Golem."

Before they began manufacturing the Golem, Rem explained why they hadn't been able to analyze the core fully.

[This core cannot be placed in an artificial container. It will not activate that way. It lacks the ability to receive orders from an outside source and act upon them. Its only function is to increase a Golem's abilities.]

"...Huh?"

"Aren't cores designed to allow someone to control them?" asked Kratia.

"Did I damage a key function when I turned it into bones? No, there's no way."

At this point, the two were halfway panicking and began interrogating...