This question gets asked WAY too much. It's not that hard to understand...Kushina was pregnant in the majority of her flashbacks so that's why she didn't go on missions and with your husband as the Hokage you also have pretty good financial stability. Sakura has to raise Sarada all on her own (unless she hires a maid or nanny there is no one else who can clean, cook and take care of Sarada), though she probably does work as a medic ninja in the village. and Hinata has to raise TWO children. One is who is much younger than the other. Naruto isn't always there so her work load is much more during the day...Ino can go on missions because Sai is there to take care of Inojin. Ino and Sai split the responsibility of taking care of Inojin evenly.
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Though something to keep in mind is that we haven't seen much of their daily lives. Naruto Gaiden took place in a few days after all. Also even if the mothers aren't going on missions they could still be doing other shinobi things...like TenTen is supervising the Chunin Exams with Lee.