Activity-hours aren't fungible and have constraints. If I need to eat by 6pm and get home from work at 5:30 pm, I generally can't just choose to swap a 9 - 10 pm hour of streaming with an hour of preparing food.
While some people can level up and perform food-prep activities during the 9-10 pm hour so that the following 5:30 - 6 pm slot can be filled with quick prep, many people don't know how to do so, nor see the ROI for such activity.