Because you get far higher ROI for the large-scale installations. In case you weren't familiar, Canada has a lot of other things which need the money than paying 5x per watt to subsidize panels on your roof instead of on the ground.
Right, but as always, ROI is hardly the most important thing in life, there is more considerations than just "makes more money". For example, as someone affected by a day long country-wide electricity outage where essentially the entire country was without electricity and internet for ~14 hours or something, decentralizing energy across the country seems much more important, than optimizing for the highest ROI.
But again, this is highly contextual and depends, I'm not as sure as you that there are absolute answers to these things.
Decentralizing through subsidies at the homeowner level is maybe not the best use of money.
Consider the lower production cost of renewable electricity: in the long run, it offsets the investment. Bonus: no risk of accidents, no hazardous waste, no dependence on a fuel source, no weapons proliferation...
Decentralizing solar power reduces electricity transmission costs and improves reliability. This doesn't offset the additional cost, but it's not negligible.
If you personally have battery backup, that helps you personally and you should pay for it, just like you might pay extra to turn up the heat while I keep it lower to save money.