I disagree that this was a sudden change, this was first discussed in the March 20th TSC meeting:
After talking to several members of the Autoware community and the Autoware Foundation, Geoff and I agreed to move Autoware.AI to Gitlab, partly to ease the collaboration with Autoware.Auto, but most importantly because the tools that Gitlab provides are excellent for big projects, such as Autoware itself. These tools will help us evolve and plan the project much more effectively.