Why are market orders blocked for trade-to-trade and debt category instruments?

Market orders are restricted for trade-to-trade and debt instruments because these securities are typically illiquid, meaning they have wide bid-ask spreads. Placing a market order for such instruments could result in trades at unfavorable prices, potentially causing unexpected losses.

The bid/ask prices often differ significantly from the last traded price, so using a limit order provides better control over execution price and prevents price slippage.