Calling it a subsidy makes it seem like it's something governments are doing on purpose. That they can easily say "this subsidy has expired, we're not giving it to you anymore". That is not the case.

Implementing a new tax for CO2 emissions is a much, much bigger political endeavour than simply letting a subsidy expire and not renewing it.

That's why there's not much value in perverting language to somehow argue that fossil fuels are subsidised. They are not, there's no way to "remove subsidies from their dirtier competitors", as the parent poster suggested.

There is a way to tax CO2 emissions, but that's a different discussion altogether.