That will be one law that will never change, because it would cause a large percentage of child support cases to increase and new laws would be created directly because of this one new law.
For example. If this rich guy has an ex and he paying child support. His salary would go up because he married your ex so his child support to his ex would be higher. So two new court case are created. Now if you marry another court case is open and if the woman you married has a child another court case is created.And if her ex get married...
Also if you can modify a child support case for remarry it has to go both way. Marriage that results in more income and then the person with the additional income loses their job. Or get a higher paying job.
It would open up the door for a ton of new child support court case modifications. Lawyers would be the only ones who love it and the small few who don't remarry but their ex spouse does to a wealthier person.
That law will never change.