First, most plates move a couple of centimeters per year, and the fastest plates (those in Australia) move around 7-10 cm. The default precision plus code is 13x13 meters, so it should take a long time to be wrong.
Secondly, one aim is for this to be an addressing solution in places without street names. If the point doesn't exactly align with the house, if they have a sign, it's still going to be easy to get the right place.
Nice question though!
[edit: move corrected to most]
If you move a house (say, a trailer home) from Nebraska to Oregon, you wouldn't expect the location to stay the same.
OLC encodes position on the globe (basically angles), not points on the crust or other territorial features.
Plus codes are not street addresses.
One of the main use cases for plus codes is to be a street address in places for which street addresses are challenging.
To put it another way - we almost always use co-ordinates to help us find a particular physical object (peak of mountain, end of runway, house on street). Co-ordinates that shift with tectonic movement are most useful for that.
I'd even argue that especially in those catastrophic scenarios, location (as in GPS coordinates) is still more important than addresses that depend on physical features (like a street) that may simply be gone.