Just my speculation, but I think that part of the reason that Janelle and Kody's relationship improved once the show started and they moved to Vegas was because:
-
Neither of them had 9 to 5 jobs anymore so they had more time to spend together.
-
Their new job was a TV show that paid them a ton of money, so their time together was less stressful.
-
The combination of money and free time allowed them to do things they wanted to do, but previously couldn't.
-
They mutually liked and enjoyed each other which allowed these benefits to create a better romantic relationship.
-
By having each family unit live separately rather than wall to wall with each other, there were fewer direct conflicts and resentments that would hurt their relationship (ex. Siding with Meri on whatever she threw a fit about bc caving was easier than fighting).
In contrast, while Meri and Christine had four of those benefits as well, Kody didn't particularly like or enjoy them. I think he enjoyed Christine more than Meri since their kids said they would dance together in the kitchen on his nights at their house and Gwen said they were buddies. But he also dealt with jealousy over her overshadowing him since she has such an extroverted personality.
Anyway, I think it's funny that Janelle didn't think Kody needed a space for his belongings in her home until they got to Vegas It's up there with her forgetting to get him a Christmas stocking even though she got them for Michelle and the dog.