Then you have the other things about Transformers- not every kid is going to automatically want Prime. Look at the way most of us as fans are about our favorite characters and the number of us who decided on that favorite as kids.
Yes Prime is the father figure, but Bulkhead is the "big brother" character of that show. How many kids are going to gravitate towards him.
Heck if it were just about the toys and leader characters, noone would give 2 hoots about Bludgeon, or even Fangry for that matter. It wasn't 20 year olds and 30 year olds who were making either popular at the time either.
This is the problem with Hasbro and retailers though- they simply can't seem to get their heads around the fact that they're not just selling children's playthings, but also pieces of modern mythology due to the nature of toy cartoons.