With respect to refundability, I would first note that refundable tax credits are used in very limited circumstances in our income tax system, when there is a clear policy rationale to do so. The working income tax benefit, for instance, is refundable because it is directed at low-income individuals.
The intention is to create an incentive for these people to enter or stay in the labour force, so it makes sense that this credit be refundable. Otherwise, when credits are there to recognize specific expenses or a reduced ability to pay tax, or specific circumstances of taxpayers' situations, then these credits are generally non-refundable. That's the general policy.