Ordinary backups don't aim to replace the full service. When you have a stock of food, you don't have enough to last you a lifetime. You have enough to weather a storm. The equivalent for tech would probably be having an offline copy of your "essential" data, but not of every photo you ever took. It would protect you from temporary internet disruption, or if a provider suspended you for a few days, but not if they banned you completely with no recourse.