The PA system is used to announce to the cabin non-trivial details: emergency exits, how the safety features of the airplane work, what is expected of passengers during the flight, flight times, expected turbulence, late arrivals, etc. These are not "mundane" details.
As well as stuff like how much drinks cost, what you might see out the left side of the plane, where to find a catalog of ridiculous items you would never buy, etc.
I thought the point of the high volume was to get thru to the people who were ignoring it because they already know the message.
The point isn't to not do the presentation, the point is to acknowledge that most people ignoring it don't need it and hence there isn't a need to YELL IT SO LOUD OVER THE PA THAT EVERYONE IS AT RISK OF HEARING DAMAGE.