Why are Stop Loss/Take Profit orders unavailable for market orders/individual positions?

If you have a US account, the following broker restrictions apply:

• Placing a market order with Stop Loss/Take Profit orders is not available.
• It is not possible to add Stop Loss/Take Profit orders to each individual position. Adding Stop Loss/Take Profit orders is only possible to a Net position.
• As a consequence: after the execution of a limit/stop order that has Stop Loss/Take Profit orders, these Stop Loss/Take Profit orders turn into a pair of linked OCO orders, but they are no longer linked to the opened individual position.