According to Halo Community Director Brian Jarrard, Seasonal Cutscenes for Halo Infinite has been cut. His full tweet explains the situation:
PSA: As we've refined our top priorities and shifted resources internally this year, we had to make the decision to forego seasonal narrative cutscenes to make room for the team to continue focusing on highly requested features, content, and improvements for Halo Infinite.
These trade-offs are never easy to make, and we truly appreciate your support as the team works to make Halo Infinite the best experience possible. While the job is far from over, Season 4 marks another big step forward and we remain committed to this journey with the Halo community.