While not representing a majority of Canadians, there are people living in regions that get regularly cold enough for heat pumps to be inadequate. Which means running a standard electric furnace (expensive and inefficient) during the coldest months of the year. Which... is not ideal, especially for lower-income rural persons. (IE, most people living in these regions of Canada.)
The rebate is great, but there are persons for whom it is insufficient.
Do I think that's a good reason to remove the carbon tax from heating fuels? No, not really. (Assuming I understand how the tax works, it really isn't the burden people expect it to be. (You can debate about inefficiencies, but as far as manipulating economics to incentivize transfer away from fossil fuels without harming the general public, it's reasonably sound.)) But people do have legitimate concerns that shouldn't be trivially dismissed.