Disc sales are now roughly half of what digital sales are, and both categories are dwarfed by subscription streaming, which in total brings in more revenue now than disc sales did at their highest peak. They don’t need to push people away from discs; the evolution of technology already did that...
Commentaries for new releases are generally recorded around the time of a film’s premiere. With Gerwig serving as a writer on the film, and the writer’s guild on strike, her union obligations may have limited her availability for recording one.