Unfortunately, it's not just apt install insulation (wouldn't that be nice?), its a multifaceted problem involving energy sources (especially if you're shutting one down), heating infrastructure, housing stock retrofits, money, and more money.
The whole story about my house was just to try illustrating the difficulty of reducing a problem to "add insulation" and the downsides of ripping out otherwise-working infrastructure.
Adding insulation has complications, but not as many as you're making it out to have. You're making it sound like adding insulation requires replacing your heating system, and it definitely doesn't.
Making it just "add insulation" doesn't reduce the problem to trivial levels, but it does reduce the problem significantly.
The whole story about my house was just to try illustrating the difficulty of reducing a problem to "add insulation" and the downsides of ripping out otherwise-working infrastructure.