People understand the transactional model because that's how most things in life work. It's only natural that people would try to attach that to Christianity however living a life serving God does not work that way. However I do see your point in going to heaven; If we believe in God and that Jesus died for our sins, we go to heaven so I guess that could be considered transactional. However I don't think as Christians going to heaven should be our main goal, serving God should.