I am not Spock wrote:
This was an even better love letter to the show than the 50th anniversary special
Well, "The Day of the Doctor" had to be more than just a "love letter" to the past; it also had to be a resolution and advancement of the arcs of the current series. AAiSaT, by contrast, was able to be more fundamentally about paying tribute to the show's history. So the two had different priorities, doing complementary things rather than trying to do the same thing with different levels of success.