but the input is 1000C, then it cool down to -700C, then the turbine compress to some 100C, then it mix with fuel and burn. why not bypass the turbine at that

but the input is 1000C, then it cool down to -700C, then the turbine compress to some 100C, then it mix with fuel and burn. why not bypass the turbine at that point and take it easy on the cooling?