Why? It doesn't say you need to have extensive experience with them. I would assume this is mostly to dissuade applicants that are not aware of the potential challenges ahead.
This "exploring" can take tremendous amounts of time, depending on the complexity of these APIs. My time is worth a lot to myself. I am not going to spend many hours for a chance of winning 5k$. If this takes a week off of my free time its not worth 5k to me.