They might also be getting conflicting instructions from different people on the OC, while the SM is (supposed to) act on behalf of the OC via resolved instructions.
We’ve had a couple of instances here where ordinary owners have acted as if they were the committee chairs when they weren’t – one wasn’t even an owner, he was bullying people on behalf of his daughter. I wish it were not so, but I totally understand why service providers might only want to deal with the strata manager.