Because they're bitter that they started working on a game that had a dedicated fanbase and over the years the fans have had an overwhelmingly negative reaction to the "improvements" the hack teams have made to it across the board. This is why they started making Marathon, so they could make something in their true vision. They proceeded to neglect Destiny 2 both because they don't care, as they see it as a hold-over artifact title made by people so much "worse and lesser" than them, and because they want it to slowly die off to push people to their pet project. When Marathon got exposed as being complete trash, they tripled down on killing D2 out of spite.
t. Knower