They have more of those parts than they can handle.
It seems that a large quantity of materials were set aside for me, but still the turtle has way too many materials for the town to get rid of all of them.
“I am overstocked on those materials. If you pay a little money, I can make a lot of stuff for you.” (Old Man)
“Is that alright with you?” (Naofumi)
“Don’t worry, if it’s a request from you, I’ll definitely carry it out. I also want to experiment with unknown materials.” (Old Man)
“…” (Naofumi)