UK supermarkets stats in 2019 showed some 1.5 billion used in 2019. That is 57 or household every year. So the vast majority are just throwing them away. Most likely they just don't want to carry them around and opt out to buy new ones. This is particularly likely if you use public transportation I suspect.

The "reusable" bags sold at supermarkets in Canada at least are really shitty. You're lucky to get 5 uses before the handles rip off or groceries punch right through the flimsy plastic fabric.

If you're serious about reusing bags you buy your own well made bags, but if you forgot to bring them or made an impulse buy congratulations, you now own a set of overpriced, very low quality bags... At least you'll be rid of them in a week or two lol

I use them for tasks like giving away vegetables from my garden but honestly that was a fine use for the "non-reusable" bags, we reused them constantly. They even got recycled into deck boards, the new "reusable" ones just end up in the dump.