Come on guys - it might not suit you but why be so derogatory? As my Nan always says, “It wouldn’t do for us all to be the same”.
From an environmental point of view it’s quite a good idea to turn old, clean, non-degradable plastic bags into stronger, reusable, hand-knitted or hand-crocheted (therefore very little extra energy input) shopping bags.
I doubt the process would be as enjoyable as knitting with yarn but I think you could get interesting results with their own kind of beauty, and “plarn” is probably stronger and less stretchy when knitted, so better for bags.
If people are knitting like this and enjoying making useful things from “rubbish”, what’s not to like? I enjoy trying to find new uses for things that would get chucked out too, it’s actually a very creative process, and I’ve been thinking of having a go at this for a while - probably shall do sometime.