Not everybody onboard is a FTer that can recite the briefing by heart. The majority of fliers, especially the last few weeks of the year, are infrequent/first time fliers. Many times, I've seen other PAX pay very close attention to the FAs announcement and studying the safety card.

The safety announcement is there for a reason. And as is always reminded on FT, FAs' primary job is to ensure the safety of PAX. If they overlook the briefing, what else is being forgotten?

Heck, with different variations of aircraft (such as 757), it might be helpful to FAs to do the briefing to know where and what type of exits are on the plane they are working.