Part of it is that servers, hard drive space and
bandwidth are much, much less expensive than they were several years
ago. Cheap webhosting providers capitalize on this.
Another part is that cheap hosting providers use a different business model than the older providers. Webhosting is a very competitive business. Until recently, web hosts attempted to compete by providing the most tools and features. The problem with this model is that not everyone needs everything. Most web hosts provide free backup services to all of their clients. Backups are costly, and not everyone needs or wants them, but everyone pays for them because they're built into the cost of the package.
A cheap webhosting provider, on the other hand, might give you the basic features that everyone uses, but offer weekly backups as an available add on feature, putting the cost of backing up websites on only those customers who want that service.
Another part is that cheap hosting providers use a different business model than the older providers. Webhosting is a very competitive business. Until recently, web hosts attempted to compete by providing the most tools and features. The problem with this model is that not everyone needs everything. Most web hosts provide free backup services to all of their clients. Backups are costly, and not everyone needs or wants them, but everyone pays for them because they're built into the cost of the package.
A cheap webhosting provider, on the other hand, might give you the basic features that everyone uses, but offer weekly backups as an available add on feature, putting the cost of backing up websites on only those customers who want that service.