Why did the elites art style change from trailer?

Games Halo 5: Guardians
1

So I was rewatching one of the old halo 5 trailers and I noticed that the elites have their original art style and mandibles which looked very similar to the Halo Wars 2 art style. Why did they change this from the Halo 4 style of elites back to the original and then back to the 4 style? This design looks so much more sleek and ‘elite’ so I don’t understand why they would keep changing it.

Halo 5 trailer with original elites (at 0:07):
https://youtu.be/1G2uz26smY0?t=7s

Halo 5 final game elite (Most of this cutscene at 34:38):
https://youtu.be/045YSXes5yI?t=34m38s

2

Those were cutscenes that were made alongside Halo 2: Anniversary, as opposed being made for Halo 5. As a result of the two games using different assets, the Sangheili look different.