How did Jefferson, in 1810 out of office only a year, explain his reluctance to

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. "