one big reason is they are bloody ugly and are drowning in unwanted electrical gimmicks

I have had my bike since it was 18 months old saving 4k on list price.  I still have it 6.5 years later having paid cash at the start.  Did all the OEM servicing myself.  Local Dealer won't trade with me.  I am happy to keep it as it owes me nothing and has given me nearly 40,000 miles of joy.  Net result is I won't buy a new bike from any dealer now so they lose out anyway.

Motorcycle prices ( new) are so competitive now it is very difficult to get a reasonable part ex on ANY bike. Market is flooded, more bikes than customers. Only way to go is sell your bike privately and buy the same. Dealers are struggling with margins. In most cases not their fault, but does not bode well for them, and us for spares and services.

Harley sportster s fetching 10k in the uk