There can be a marriage penalty, but married people also have more options to file their taxes and a host of other benefits we shouldn't ignore in this discussion. For example; cheaper insurance, Social Security benefits, family leave, veteran's/military benefits, estate planning benefits/exemptions, are direct monetary benefits. Along with a host of legal benefits like visiting rights, immigration/residency rights, divorce rights, medical decisions and ICU visitation.
[1] https://www.nolo.com/legal-encyclopedia/marriage-rights-bene...