You are making the baseline assumption that the reason for reusable bags is to reduce greenhouse emissions, instead of reducing the number of plastic bags being discarded in public areas causing negative externalities like affecting wildlife. Heavier plastic bags have a greater chance of lasting beyond a single shop trip to make it long enough to be reused at the very least as a garbage bag. Paper bags desintegrate easily if thrown in the trash and are trivially recyclable.

I do think that we need to meet people where they are at, you can't expect people to over night start bringing a classic trolley and/or canvas bags to a local shop if they don't have a shop to walk to or dont have a way to keep a bag on themselves at all times, but we can slowly nudge people towards desirable behavior. And that's what charging for bags does.