Well, nothing, I would imagine; but keep in mind you are locking away a lot of money for a very long period of time, and the payouts are constantly adjusted with age—so unless the companies are outright screwing up and allowing an arbitrage opportunity, you reduce your expected returns either through not getting as much ‘relatively’ as you seem to expect or by opportunity cost (the companies returning your money, but having profited off the ‘float’ - which is how insurance companies have long been able to pay out ‘more’ than they should, because they made their profit off investing your money and not taking a percentage of your premiums).
Well, nothing, I would imagine; but keep in mind you are locking away a lot of money for a very long period of time, and the payouts are constantly adjusted with age—so unless the companies are outright screwing up and allowing an arbitrage opportunity, you reduce your expected returns either through not getting as much ‘relatively’ as you seem to expect or by opportunity cost (the companies returning your money, but having profited off the ‘float’ - which is how insurance companies have long been able to pay out ‘more’ than they should, because they made their profit off investing your money and not taking a percentage of your premiums).