Yes, you cannot force the due diligence nor common sense ... unfortunately, but then there is the Darwin Award ...
I'm sorry but that is a poor answer. Especially to pull the "Darwin Award" card on sUAV operators in THIS particular instance.
There are going to be many times that you try to call a tower and they will not answer. They get busy with aircraft that have souls on board.
Maybe the tower in question here is not so busy, but many of us are near airports that have constant traffic and a heavy load.
Most towers will not have time to deal with numerous calls about sUAV activity.
They will simply expect you to use due diligence and common sense to follow the guidelines whether you get through to them or not.
Trust me, they are not hanging on the edge of their seats waiting for one of us to call.
There will also be times that an sUAV operator forgets to call back or is distracted and doesn't call back.
Those are not grounds for "Darwin awards". It's human nature and ATC has to work in those parameters.
You are NOT going to get sUAV operators to act as though they are in the ATC system.
Most do not know the system at all.
It's not about due diligence, it's about what happens in the real world.
Besides, the OP stated he was happy to oblige.