Pretty much no dealer but bmw, Ducati or Harley will have a demo bike available. I once asked and was told it was due to insurance.
@bigpoppa was nice enough to inform us that Apex Cycle in Cambridge has some demo models available for different brands.
Also COVID-era high demand/low supply situation means they don't have to give out any test rides and people will still buy their motorcycles.
Pre-COVID, I rode into Maranello Motorrad and asked for a test ride and they were throwing keys at me like: