I think that's because it's adding to the cost of solar, effectively making it an barrier to entry; when other provinces or states have financial incentives to install solar panels instead.

This measure sounds a bit disingenuous since Alberta has such a large petroleum industry and this type of measure targets in particular renewables, it looks like a punitive tax. If the problem really is recycling costs, make them payable on recycling (like, again, many products such as used drywall or oil)