How does a burnout ruin your motor?

To say that a burnout alone ruins your motor seems a bit far fetched. If you power brake to start the burnout, it can wear your front brakes out which can cause dangerous fish tail skidding later. If you rev the engine high and pop the clutch to start the burnout, then you stand the chance of breaking an axle, dropping a drive shaft, or other things in the driveline. The only thing I can see really having potential to ruin your engine in a burnout is over revving the engine. Some let their adreniline get away from them and don't realize they are at or over red lining the engine and holding an engine in this state can cause things to start to come apart internally.