The role of the tower is to separate aircraft in their control zone, not just on the runway, but this is kind of where it gets tricky by definition.
We are only required to provide conflict resolution to VFR aircraft in Class C upon request but they will always be provided traffic information to assist in achieving visual separation. The whole "upon request" thing is silly though. We're not crazy enough to let a situation deteriorate to no return and not say anything about it. We don't have to provide conflict resolution but how can we, in good conscience, let two planes come so close and not do anything about it?
Above the zone is Class E, so no conflict resolution and traffic is workload permitting but everyone wants to call and expect service. We technically don't have to provide any kind of service in Class E, but again... in good conscience, how can we let two planes come that close and not say anything? Our focus and priority is always aircraft in our control zone, so airplanes in the Class E sometimes get ignored
That's a very harsh way to describe it Phraseology is a set standard, but we are allowed to communicate using plain English... and definitely no punishment handed out, otherwise I'd be out of a job already.
Those annoyed pilots need to review their airspace classifications!
It's all about workload and how more airplanes on your frequency will inevitably take up a controller's time and attention away from their primary role - very similar to airplanes calling up requesting service in Class E airspace. Terminal controllers are all about providing IFR service first and foremost. Vancouver won't entertain most requests because they are busy working airplanes within a very confined Terminal airspace. Pilots aren't expected to know our procedures so while being told to remain clear sounds harsh, it's probably because your request may bring you nose to nose or into the wake of a 747 joining the downwind for Vancouver.