2. material (for a novel, experiment, etc.); subject matter
たぶん、書くべき材料がそれほどなかったからだろう。Probably because there wasn't much material to write about.
3. grounds (for a decision, judgement, etc.); basis; evidence; data
交渉材料として使える。It can be used as a bargaining chip.
4. (market) factor