“Bush suspended his campaign before those primaries.”
Bush suspended his campaign in May of that year. Reagan was getting 60%+ in most of the primaries prior to that.
In the less urban states, yes, but Bush had done well in more urban states, winning Pennsylvania, Michigan and others.
I'm not sure what the argument is about, though. I was just pointing out that those last 12 primaries did happen after Bush stopped campaigning, so the party wasn't as united behind Reagan as the numbers might indicate.
In any case, it wasn't party loyalists Reagan was worried about, but the swing voters who might still go with Carter. That's why he had to pick a running mate who was thought to be more "moderate."