They're also better for stability in numbers of employees, as it's easier to reduce expenses in bad years without having to go through layoffs.
Admittedly, there might be other, additional causes to this. It should still be considered if higher turn over is a business risk for the company.
In an ideal world, people would be a bit better about managing uncertainty and most people would be able to live comfortably within their means on their base salaries and would have the restraint to invest large percentages of their bonuses.