Adding insulation will definitely help IF the ceiling was not secured to anything at the ends and/or sides as they should have been. Otherwise likely a waste of money.
You can easily see in the attic if they were not every 4 (or 8) feet at the seams.
I imagine after a thousand complaints they changed the construction methods on new homes.

It makes sense that normally the lanai and garage were not insulated above since it is non-conditioned space. If only they secured properly. It was said that building code was followed. I find that questionable. If I find the POA (Property Owners Association) final report on this I'll pass it along. It was a couple of years ago.

Insulation is only installed to create a heat transfer barrier between a conditioned and an unconditioned space. The garage and the attic above it are both unconditioned spaces, therefore, there is no need to install insulation. Same for the lanai. Adding insulation above the lanai and garage would be a waste of money. Also, I don't think it will do anything to prevent ceiling cracks.