#4 To protect the Jackhammer
A certain section of the fans dubbed the smarks or smart marks (you and I may very well be among them) know that Goldberg isn't necessarily Ric Flair in the ring, and that he has to be carried by his opponent more often than not. But there is a vast population that still loves and cherishes Goldberg and may be lapsed fans who will tune in to watch the show, now that Goldberg is Champion again.
It is very clear if you look at WWE as an organization, that they do not merely wish to appease the fans that they have, but grow their fanbase. Goldberg is a marketable name and also a familiar name, who will certainly connect with a lot more people than The Fiend will, at the moment.
A WWE Hall of Famer isn't a John Cena fan. More details HERE
And for the same reason, unlike Seth Rollins' curb stomp, WWE couldn't have Goldberg's finisher seem absolutely meaningless. If nothing else, WWE has a long-term deal with Saudi Arabia and one assumes that Goldberg will be on the cards for various appearances in the near future, so after kicking out of multiple spears, the Jackhammer needed to be protected by the company.