Exactly - it is an argument for continuing to use coal, because we have valuable infrastructure even though we know how bad it is for the environment. Which explains why it is so hard to stop using coal.
In the US, the share of power being generated by coal has fallen from 50% in 2005 to 20% in 2022. (In absolute terms, which is what really matters in an emissions context, it's fallen from 2T kwh to 0.75.) To phase out existing infrastructure just takes incentives and time (and 18 years isn't even that much time on the scale of infrastructure investments). The same can happen to methane infrastructure, especially since non-fossil alternatives are far more viable than they were when coal began to be phased out.
And the US has stopped building new coal fired power plants, so a decay to zero is just a matter of time (although it could and should be accelerated.)