Ok I have to admit I just watched the first 3 episodes of the first season, and I think that these folks have been raised in this enviroment, all those wives grew up in homes that were the same way.
I do think it might be nice to have someone share the workload around home, and have someone handy to watch my kids so I could have a special evening once a week with my H.
I have often joked that if there were another time for M'ing I would get a wife, I want someone to do my laundry, cooking, cleaning, and grocery shopping.
As far as each wife getting younger that goes with the whole religions philosophy, and that is to make as many offspring as possible. If you marry older women, that doesn't work. They believe making more and more babies is Gods will, and that's half the reason this lifestyle exists, because all of our girl parts have experation dates.