Austin also seems by far the closest BIL to the rest of the Duggar siblings. Jeremy looks down on the Duggars, Ben doesn't seem close with any of them, and Derick wants nothing to do with them.
Meanwhile, JD, Jed, and Justin all had Austin as a groomsman in their weddings. Joy was close with her brothers growing up, and now she has a husband who is close with them too. Another reason she appears happier in her marriage than the others.
Like everyone else, I hope Joy isn't pregnant every year, and gets to enjoy her family of four and pursuing softball + her other hobbies.