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.