[nikos1121]

why would he try to have his conviction over turned if he was pardoned?

[Alberta's Child]

From a prior (8/29/17) article from Tucson.com explaining why Arpaio's lawyers would prefer to have the conviction overturned than negated via the pardon:

For example, they [Arpaio's attorneys] cited court rulings that said this conviction could be used against him at the time of sentencing if he is ever found guilty of any other crime. That could result in a stiffer sentence.