You're missing the point. if you push out cap into future years with signing bonuses, you'll have less money in those future years than if you don't. This gets worse when you factor in that when you don't push out cap you can get rid of underperforming players and bring in better players with the money you have extra due to less dead space. Add to that injuries and trades as being more problematic because they can accelerate cap and you start to see why large signing bonuses to push out cap are riskier.