Why do you think he decided that land in outlying provinces should be given to relatives? Why do you think he believed relatives were best for this job?

The correct answer to this open question is the following.

You did not include any reference or context for this question. You did not say the name of the individual you are referring to.

However, doing some research we can comment on the following.

First, we are talking about the Second Tang Dynasty and his emperor Taizong. So Taizong is the character referred to in these questions. He was a good emperor and ruled from 626 to 649.

I think he decided that land in outlying provinces should be given to relatives because the territory that had to be defended was enormous and the responsability to defend the land. So as China was an immense territory, the emperor had to give portions of land to the relatives so they could take care of and defend the provinces.

I think he believed relatives were best for this job because the emperor could trust them in good and bad times. The emperor needed loyalty and this was the best way to get it. Committed relatives would impede invasions and rebellions.