slab no cracks: Brick veneer cracks

Here is a general question about some issues I have seen in some homes.
The foundation is slab-on-grade.
Exterior walls are brick veneer.
The slab appears to be is excellent condition, only minor shrinkage cracks and corner pops if anything
But the brick veneer has some moderate size cracks (they appear to be old cracks).
One house had sister cracks (west and east walls) but no cracks in the slab.
What would cause this to happen?

My first thought is down-warping of the slab.
I seem to remember someone talking about this caused be shrinkage in the structural members, but that would be difficult to explain the sister cracks.

Any ideas?

Mortar for the bricks during installation could have been defective (not mixed right, sat too long, etc.)

Are any of the cracks above windows or doors? If so it could be a faulty lintel.