Tradition, and the need to call it something.

"What are the limitations of profit and loss account?"

Profit and loss accont is used to calculate the profit or loss of business while profit and loss appropriation account is used to allocate or distribute net income or loss to share holders or different reserves account.

Income and expense for not for profit organisations is same as profit and loss account but they cannot use the name profit and loss account because not for profit organisations are not formed to earn profit.

Debit balance of Profit & Loss Account represents "Loss"