Why cutting torch cannot cut Aluminum sheet?

because it will heats the steal to a molten state or it ignites the steel to burn through the kerf of your cut.

Because Fusion coefficient of aluminum is law & didin't bear the high heat of cutting torch , aluminum egdes will burn.

Because a torch will literally melt the aluminium part and will not retain the evenness as we see in cutting the sheet metal part of stainless steel.