Why Gain on sale of fixed assets is subtracted from Cash generated from Operating Cash flow?

Gain on sale of fixed asset does not point to the exact amount of cash that company receives as it is calculated on accrual basis (including setting off dep..which itself a non cash exp). therfore to negate the effect in cash flow statement we subtract the gain on sale of asset and instead add the actual amount that the company receives under investing activities.

This is not a regular transactions and not any effect on operating activities of daily business. Cash from operating activities will only include the types of transactions which is related to daily business operation.