From my understanding of it, Until, you could get a piece of the family benefit if you care for a child of the SSDI recipient (so instead of 2 kids splitting 50/50 the maximum of 50% of hubby's benefit, you and 2 kids would each get 1/3) Frequently, the spouse of the SSDI recipient is in a higher tax bracket than their kids so they choose to just keep the split between the kids.

I've really only heard of ex spouses of the SSDI recipient wanting it divided that way