The VA and Helping Veterans Cast a Vote

I missed this NYT Op-Ed piece from last week. Why would a VA Secretary ban nonpartisan voter registration? I cannot think of one legitimate reason for a blanket ban.

The department has placed an illegitimate obstacle in the way of election
officials across the country and, more important, in the way of veterans who
want to vote. A group of 21 secretaries of state — Republicans and Democrats
throughout the country, led by me and my counterpart in Washington State, Sam
Reed — has asked Secretary Peake to lift his department’s ridiculous ban on
voter registration drives.

Why are we making it more difficult to register and vote for the very people who risked much to guarantee our right to vote.