The idea that people are using reusable shopping bags because they want to virtue signal and not because of any actual desire to do good is a completely baseless and needlessly pessimistic viewpoint. A much more reasonable and likely explanation is that most people can't fully assess the environmental impact of their decisions, so they make the entirely reasonable assumption that if they can avoid throwing away a dozen plastic bags every week, then that's probably a good thing. That assumption may turn out to be incorrect, but that doesn't mean they have the harmful motivations you are accusing them of.
No, such people generally do think they are doing something worthwhile, and worthwhile things are right to do.
If, in fact, they are not doing anything worthwhile, which this graph suggests, then that is a mistake of the facts. It doesn't mean that they were just trying to "virtue signal."
The higher number come from value judgements about other kids of impacts, and reasonable people can disagree over the relative values of those impacts vs climate change.
They’re not a little bit better - they’re dramatically worse.
I’m not saying I have a solution either but not acknowledging that it’s a systemic problem is fairly thought ending.
I think this is a side-effect that provides positive feedback, just like many of these initiatives, they are a way for rich people to feel like something is being done without doing anything, while actively maintaining their position in the world. If you look around, there is a lot of stuff like this.
Does it help? In the grand scheme of things, it won't help enough, but waste reduction is always helpful.
What is your solution?
We're like drunk people search for our keys under the streetlight - we only focus on the stuff that we can see, rather than what is actually important.