For the same reason they pay for online referrals - it's an avenue that drives sales their way. No charity involved. As for the pricing at b&m stores, at least

For the same reason they pay for online referrals - it's an avenue that drives sales their way. No charity involved. As for the pricing at b&m stores, at least in the case of smaller shops, they simply don't have the ability to price anywhere near Amazon. They don't have the leverage to negotiate low enough prices from publishers and distributors. B&N I don't know about. I'd think they could discount somewhat more, even in store.