Because he believed politics negatively affect his mental health.
Explanation:
In 1810, he sent a letter to one of his friend. A man named David Howell.
In that letter, he briefly implied how hard it is to be a high ranking government officials. Having to made all kinds of decision that will benefit a certain group of people while causing problems to the other. It's exhausting.
This is the reason of his reluctance to engage in political topics. He wanted to take a break from all of it.
To proof this point, I will quote the things that He stated in that letter:
"My object too at present is peace and tranquility, neither doing nor saying any thing to be quoted, or to make me the subject of newspaper disquisitions. "