The original intent behind alimony was to compensate a homemaker who had put their career on hold and essentially trashed their resume. They’d permanently hobbled their earning potential for the marriage and the marriage fell apart.
It only became possible to even think of alimony as supplemental income in the 90s and early 2000s when judges were handing decisions to women almost as a matter of course. It took a decade or two before divorce courts (and family courts) started to chill out and look at things a little more objectively, but even during the bad old days infidelity was the one thing that every single judge would throw the book at you for.
It’s just so fucking painful to imagine. Being cheated on feels fucking awful. Then having to permanently pay someone who did that to you. Also, if that cheating was the cause of the divorce, then that means they’re not just taking money from you, that person took your marriage from you.
So you’re sexually violated, lose your most valuable relationship, and then you have to pay the person who did it to you like they’re your landlord.