Answer:
Savers make deposits and investment in order to earn interest on their money. This often works very well because they do not earn only interest as a percentage of their money, but also interest as a percentage of previously accrued interest, something known as compound interest.
Savers do not invest their money directly with the businesses because real economic activity tends to be riskier (although it could also be more profitable for this same reason). This is why they often prefer to invest the money on financial instruments.