I was thinking about this recently, and I think that we sort of mis-remember the sister-mom role. Jill provided some affection and attention to her buddies to supplement the zero attention they got from their actual mother. The sister-moms kept track of their buddies when the family was out as a group. All of the kids had other siblings to play with during the day. No one appears to have taken responsibility to see that they were fed regularly. They appear to have seldom bathed. The TTH was (is) filthy -- the kids run around INSIDE all day long, and their feet are black with dirt all the time. There are (and haven't been since the initial reveal) clean sheets on any of the beds. I don't blame the sister-moms for any of this, of course. JB and J'chelle were overwhelmed by parenthood and the responsibilities of maintaining a household back when they had 5 kids. Their response, of course, was to have 14 more.
Think about what Jill's day would be like if she was a normal homemaker.
Get up in the morning, get the kids dressed.
Find an activity for Izzy and drop Sam in a playpen while she cleans the house and/or does some laundry
Take the kids to the park or the library or a similar activity
Come home and find an activity for Izzy and drop Sam in a play pen
Clean up while Derick plays with his sons
Give the kids a bath, get them into pajamas, read them a story, and put them to bed.
Lotion time with Derick
Think about how much of that she actually does -- not much. I think her days are as aimless and chaotic as her days at the TTH. I also think the fact that she's expected to feed those kids EVERY DAY, and entertain those kids EVERY DAY, is exhausting for her. She has no experience with schedules, or routines, and I'm sure it's nearly impossible for her to figure out how she would squeeze cleaning into her "busy" day. She also has no frame of reference for what a clean, comfortable, inviting house would look or feel like.