If they were here on a non-immigrant visa then they were already found admissible to the US. Some of them were just straight up illegals (like dreamers). I've met dreamers from time to time and all of them regularized their status after marrying (I assume the ones that didn't though weren't eager to tell me about their status so I simply never found out).

One interesting note here is the case of DACA recipients. If they leave the country to adjust status it should triggers a re-entry ban unless they're granted parole (DACA are quasi-illegal but granted a form of amnesty as long as they remain in US). AFAIK parole isn't granted for US consular visits, so it's effectively banishment as punishment for trying to adjust their status to reflect their marriage.