Please explain why the answer is C

I thought for Paradox questions, the answer needs to establish why the change happened. Answer C only mentions that animals are more desirable to collectors when they're rare, however, it never mentions that the collectors do indeed collect them. It could be that these collectors desire to collect rare animals but for some reason, cannot actually collect them. If this is so, it wouldn't explain why the decline of endangered animals sped up after being listed as endangered.