I'm quite certain it is all revenue driven and keeping up with features and innovations of competitors. I would also suspect that some changes are driven by suppliers and availability of components and the cost of those components. No matter how good a design when sales become flat it takes a refresh to draw more customer interest.
That is my .02 cents worth but what do I know, I don't even own a 5th wheel. I like the Thunderbolt line but not willing to go 40' or longer, so I have been told the 340AMP is going to 38' and I may jump on that one. I have the advance sales flyer from the factory showing 38' but it hasn't shown up on their website yet.
2016 Ram 3500HD 6.7L CTD 4x4 CCSB
2017 CC 34RL2 Hathaway Edition (on order)