Because of goals in a group stage vs Panama & Tunisia and a penalty vs Colombia. To be remembered as one of the greatest ever you need more. I'm not saying he'll be forgotten, but in say 10 years when people are discussing the best strikers to ever live, I don't think he'll be up there. Playing for Spurs won't help - Zlatan only won league titles & lacked impact on the international/European stage but he played for the big clubs.
You only have to look at Kane's Ballon d'or placings to see how playing for us & lacking impact on these big European/world tournaments has impacted his standing. This will resonate with fans too, rightly or wrongly.