Any reason why this function is not available in Japanese mode? At least for a beginner such as my self it would be nice to have it in Japanese as well. Or maybe I just can't find.

The way component characters work in Japanese, they're usually not very useful (and often very confusing) for anyone who is not doing RTK.

Why are there no component characters in Chinese?

In Chinese, Chinese characters typically are used on their own more frequently and have fewer readings and definitions, so they're first class. In Japanese, many fewer characters are actually words by themselves.