That's the intentional design of the rating table. When you are in the higher OAT range above the "knee" of the rating curve, the maximum engine thrust capability of the engine is limited by the temperature the hot section can withstand due to material temperature limitations. The control system and its rating tables are designed to keep the hot section temperatures below the material limits, and that is why the thrust is rolled off with rising OAT above the "flat rated" range to achieve a roughly constant EGT above the knee of the thrust vs OAT rating curve.
The engines are built to be as light weight as possible while still delivering adequate thrust as marketed to the airframer and operator. Setting aside more subtle limiting aspects of engine design such as blade pressure loading and compressor stage pressure ratio limits, the maximum thrust a turbine engine can produce can be limited by the internal gas pressure the engine case can withstand, the rotational speed capability of the shaft system structures, or the temperature capability of the high turbine. Below the knee of the takeoff rating curve, the engine is typically case pressure limited, leading to that part of the curve being designed to provide relatively constant thrust vs temperature, with shaft speed increasing with temperature. Above the knee it is hot section temperature limited, leading to that part of the curve being designed to provide relatively constant EGT vs OAT. The MCT rating at high altitude is typically fan shaft speed limited.
Tdracer may be able to offer more as turbine engine control system integration with aircraft is his area of expertise.