Compiling code is the easy part, peripheral drivers which implement both the basic Arduino functions (digitalWrite and so on and so forth) and more advanced stu

Compiling code is the easy part, peripheral drivers which implement both the basic Arduino functions (digitalWrite and so on and so forth) and more advanced stuff like SPI/I2C, WiFi, etc. are necessary to make a working "Arduino ecosystem." I think the reason that ESP was so successful is they provided both a working Arduino standard library so that sketches could just be copy-pasted from other platforms, and a reasonably decent real RTOS-backed development environment (ESP-IDF) for once users outgrew the Arduino training wheels.