Exits are in different numbers and locations on different aircraft, and the doors can be opened in different manners. Exit routes once outside vary dependant upon aircraft configuration - although "get away from the burning/sinking plane" is pretty consistent. You cannot say the same for being a car passenger. I have seen fellow SLF who cannot operate a seat belt - I wonder how they got to the airport unassisted.
During an emergency descent I do not think the FAs are going to be able to stand in the aisle and do a safety demonstration. Also consider the SLF noise due to panic. If the oxygen masks deploy a novice passenger cannot sit there suffocating whilst told how to make the oxygen flow in the mask.
I always listen and watch the demostration, and read the card - even when I have sat in the exit row of an aircraft where I was involved in the design of the overwing door. I think the FA should be able to 'spot-quiz' any pax who has obviously not being paying attention - ask them to locate their lifevest and inflate it, ask them to locate the second nearest exit, etc.