1. Safety. One place could go burning in fire. Second place could be destroyed by some missile. It might happen simultaneously or while you're trying to retrieve the backup. So you need multiple decentralized copies to ensure safety. Also you can't just use AWS because then might ban your account and you'll lose your data.

2. Price. There are many computers with a lot of free unused storage space and unlimited internet plans. Basically storage and transfer is 0-cost for them. So they'll compete creating very affordable pricing. AWS can't compete with that, because they have real operational costs.