Why do people cross-train in such similar arts?

[drop bear]

Another advantage of training similar styles is that while it might be the same basic concept. The emphasis is on different aspects of that concept.

This means you can't cheat and rely on only what you are good at but are forced to develop a deeper game.

So sometimes times we will wrestle Roman Greco. Which means no leg grabs. So I have to go for all those hip throws I would otherwise avoid.