Serious question: who pays an effective rate of 40 percent? Many of these huge corporate entities are in the single or negative digits.
It's a 401k in the US. It's a tax deferment, not a tax break. If your effective rate went from 35% to 25% due to your 401k contribution, you still end up paying 35%, just not right now.
But if you put a lot in, the fact you HAVE to start taking money out at a certain again AND it all gets taxed before you die means you pretty much end up paying the taxes anyways (or more if rates have gone up).
A lot of them even have no idea that they will be taxed anyways when they withdraw.