Yes but if you're having a massive tidy up or, two people with fully equipped houses moving in together, or sorting out a relative's house after they've died, it's not "just" one bag of fabric, is it?
It's10 files of old paperwork
A house load of furniture
Several wardrobes full of clothes of all ages and sizes
boxes full of toys
cupboards of food
boxes of random tools
gardening paraphernalia
full sets of crockery and cutlery
shelves of books
jewellery
car/bike
carpets/rugs/curtains, light shades, bedding, etc
and whatever else.
Most of which won't be accepted by the same place. If charity shops take them at all, which they often don't, you still have to sort them out and package them and transport them.
Perhaps that woman has already done 8 charity shops runs, 10 trips to the local recycling centre, paid for several big item collections from the council, sorted BHS to collect some of the best furniture, gone through and shredded/saved 70 years of paperwork, shared expensive or sentimental items out to the family, waited around for multiple timewasters on gumtree/fb marketplace, put stuff on ebay, taken random recycling to the big bins in the supermarkets, all after dealing with probate, trying to sell a house, whilst suffering through the grief of losing a family member, and doesn't need to be judged for being "stupid or lazy" for the one flipping bag of material she didn't know what else to do with?!? Is it really such a big issue in the scheme of things?
and as for "any school, nursery, Brownies/Cubs, afterschool club would bite your arm off" - I'm a teacher and I'd have no idea what to do if someone gave me a random load of material and buttons! tbh I'd be deeply unimpressed they were trying to offload their crap onto me.