It was a last minute decision. One of the main reasons he chose Bush was because Bush was at the convention and could make it out on the stage with him in a matter of minutes (after Ford refused to play ball). There was no vetting or interviewing. He didn't have time to consider what was best for uniting the party. That's what choosing Ford was supposed to do. Reagan first broached it with Ford 5 months earlier.
Again, he should have gone with Kemp.
It almost got Reagan killed too. The Bush family being friends with the family of the assassin doesn't pass the smell test.