I wanted to know the specific details of why can't we use it? Is it because of the different architecture or the fact that ESP uses python for networking such that the compiler needs to compiler python scripts as-well because I was a python code in the ESP , SDK folder.
Please be specific by calling it ESP8266 rather than "ESP".
Those python files aren't used for normal compiling. They are for building the ESP8266 core for Arduino (get.py), testing the ESP8266 core for Arduino (build.py), and the "Classic OTA Update" technique (espota.py):
OTA Update ยท ESP8266 Arduino Core.
By "the gcc provided by the Arduino" I assume you mean avr-gcc. Yes, the reason why a different compiler is required for ESP8266 is the different architecture.