In bookkeeping why are revenues credits ?

whenever revenue  increases it is credited

BECAUSE REVENUE INCREASE OWNER EQUITY THAT IS WHY IT IS CREDIT

There r two types only one is for debit means from whom we need to get or collect back, another side is credit means already collect in shape of liability, accounts, invoices etc.

As all forms of liabilities are being booked as credit. So Revenues or sales is also a liability as containing profit element in it, and that profit is liability of the company towards its equity holders or partners.

In bookkeeping, revenues are credits because revenues cause owner's equity or stockholders' equityto increase.Recall that the accounting equation, Assets = Liabilities + Owner's Equity, must always be in balance. The asset accounts are expected to have debit balances, while the liability and owner's equity accounts are expected to have credit balances. Therefore, when a company earns revenues, it will debit an asset account (such as accounts receivable) and will need to credit another account such as Service Revenues. The credit balance in Service Revenues will eventually be moved to the sole proprietor's capital account or to a corporation's Retained Earnings account (thereby increasing the credit balance in one of those owner's or stockholders' equity accounts).

All the incomes generated by the business are credited upon realization. Furthermore, owing to the separate owner entity, the incomes realized held the business liable to pay the income to the owner who have the right on it. Since, all the liabilities are credited when increased, increase in income is also credited.