When I was shopping around Progressive wanted me to take the bike to one of their offices for some sort of inspection. Perhaps they are wary of insuring a motorcycle only to find out it's been wildly customized and made more accident prone... think big chopper with a 4" front drum brake, or even no front brakes!
Esurance should have asked you for those photos before they issued the policy. If they took your money, they shouldn't start threatening to take away the policy.
Geico didn't require any sort of inspection and their prices were good, so I went with them. Now that RI law allows antique vehicles to drive anytime as long as they have a safety inspection, I might go with a classic car/motorcycle specialty insurance and an antique license plate. Cheap and cool 8-)