HD have an image problem hence the declining sales is my take.Millennials with enough coin won't waste it on a product that represents what they aren't.All the electric bikes HD have coming will carry the baggage (badge) of a bygone era and won't have the market segment to their own so no reason to think these will halt the slump.
The Asian market push is an uphill battle with the Street 750 being annihilated by Royal Enfield with a less than half the price advantage.That Harley badge is no longer all it takes to win sales.

From a Spyder/Ryker point of view where is the competition,it's purely from within (not ideal from a consumer point of view).Thankfully the Ryker is different enough to almost guarantee it's success.Only way it could be better is if it were available with a 'I don't want the stock seat/shocks/swaybar etc give me a rebate to upgrade option'.If you add up the inevitable mods they are not millennial cheap.