I'd guess that Thor sees an opportunity to reduce supplier costs by way of higher volumes shared across many brands. Instead of contracting for 40,000 of a widget, they can likely negotiate a better price for 250,000. They can also share best practices across the different companies. An executive who is successful in one of their companies can move to another one of the Thor companies to help make that company more successful.
It's also possible that they may be thinking about vertical integration of other parts of the value chain. At some point, if you have high enough share of the market, it's going to make sense to set up or acquire your own sub-assembly or appliance company and capture the profit from that part of the value chain.
There may also come a day where there are different dealer relationships and contracts. If you control 1/2 the market with your companies and brands, maybe one day the balance of power between dealers and manufacturers will shift toward the manufacturers. That might enable a shift to auto-dealer type of warranties; something I think we'd all like to see. Wouldn't it be nice to grade dealers on quality of service and require all of your dealers to provide timely warranty service, regardless of where you purchased your rig? That could come.