You are not making sense. More players would mean more sales not less. The figures are for the whole market and not those four mentioned who have over a 10% share of the market. Besides Hymer is Roadtrek and no Hymer branded B has been sold yet. There is about another 4% unreported here and those companies simply have sold few Bs and there are none that will be threatening the top 4 entrenched mentioned in sales at least to the point of changing them much. The active market much discussed here is mostly in that 4%.
A downturn from a year ago is a bit alarming. B sales could be the "canary in the cage" bellwether. I still think with 8-10,000 Baby Boomers retiring every day and little real growth in comparison is not a positive sign. Growth is nothing like it was before the great recession and before Baby Boomers started retiring.
It could be changing demographic focus of what people seek to do and how they travel. Will internal combustion engine forsaking Millennials not adapt to RVing? It could be discouragement with little growth in campsites and more people seeking them. I wonder how many people have given up RVing when discovering it is next to impossible to get into a Florida state park campground in the winter unless you plan a year ahead. Conversely, Minnesota in the summer.
Nothing is forever. It could be people now prefer to walk around with their heads down using Pokemon Go on cell phones.

Outside of my RV friends who live mostly all over the country, the friends I've known locally for years, especially the retired my age, not a one owns an RV. We are all anomalies here in this forum.