Lucky1, the 8 degrees were a cheap buy for harley, but in a lot of cases they have issues such as cold start, poor idling and there was a Harley Tech Article or an informational given to the dealers with these type of problems. I personally have never had them in a bike so it is hearsay and if I recall there were some on this site that had posted about it and problems.
So the answer would be reliablity and avoiding possible problems. Some Harley dealers swapped out the 8's for the 25's and issues went away, some dealers never got it figured out, and have even heard of dealers giving away a Race Tuner to solve the tunability issues for the customer. If it were me and I had the 8 degrees *Delco* ones I would insist that the dealer switched them out. Others just chose to buy the 25's and avoid possible issues now and later.