We don’t know the extent of their wealth, but it seems that the husband here is in a field (probably finance, stock market) where at the end of the year, HE gets a bonus. He allocates X% for her splurge. From the bonus he likely allocates a % for his own splurge. Probably the rest is on the family’s splurge (vacation, summer home, new boat, whatever).
If you’re wealthy enough, you have a money manager, who might handle ALL the family’s finances, or who sets up a budget to give the wife $x/month to pay the mortgage or rent, household expenses, staff, kids’ tuitions, etc., etc., etc.
I don’t live in that sphere, but have known some who do. The ‘bonus’ is not an insult, it’s not demeaning nor meant to be demeaning. It’s a gift for a job well done appreciated. And its amount seems to depend on HIS bonus at his job.
In your scenario, a third party money manager, it would make more sense.
But, even if it’s just her husband who doles out the allotment..... if it works for them, and they stay married with an intact family....more power to them. Everyone is different.