The Torah uses the male form for the words, and the Sages extrapolated from here that male Amonites and Moavites are banned from the congregation, but females are not.

Going to look up the source soon.

The Torah uses the male form for the words, and the Sages extrapolated from here that male Amonites and Moavites are banned from the congregation, but females are not.

It says on Chabad's Ask the Rabbi page that the decree was made against the men because they did no go to greet the Jews with food and drink. (See Devarim 23:5.) This was not expected of the women, so the decree was not made against them. (Yevamot 76b)