Based on my personal experience over the past three decades of inspecting houses, I would say that differential brick expansion is the most common cause of cracking in brick veneer homes. The second is sag in double-wide garage door steel lintel beams. The third is steel lintel expansion. The fourth is differential foundation settlement and rounding out the list at fifth is reflective cracking.
As I’ve said many times, foundation repair contractors lump all five of these into one category: foundation settlement or foundation failure. This is literally the farthest thing from the truth when talking about cracks in brick veneer homes. We seldom see any differential foundation settlement problems that warrant expensive foundation underpinning repairs!