Maybe because men are being negatively stereotyped? And also that's not true. "Plenty" of women ARE outraged over this ad. You may need to explore outside your bubble to see them.
Not all women are single and own cats, but if the GOP put out an ad of a woman leaving the house to vote and saying goodbye to her cats (with no man around), then after casting her vote for Harris, she comes home to proudly show off her "I Voted" sticker to her cats, I would imagine "plenty" of women would be publicly outraged. And rightly so IMO.
The reality is more accurate - significantly more on the left won't date across political lines then the right.
Many single-and-looking people wouldn’t want to date someone who voted for the opposing party's candidate in the 2016 presidential election.
www.pewresearch.org