Each subject line with name in this case would print "Aaron Anderson" rather than that person's actual name. Can someone point out why this would happen?

Consider $subject. The first time into the loop, it might read  [name]! You can enlarge your whatever! Then you swap in a name, and send the first email.

So what is $subject going to be the second time through the loop?

  Aaron Anderson! You can enlarge your whatever!
[download]

There's nothing left to substitute.

It looks like you need to make copies of both $subject and $messages each trip through the loop, and expand macros in the copies.