68tjs:
But if Arduino gave possibility to volunteers to adapt other microcontrollers the conditions would be totally different.
Not only has Arduino given that possibility, they have done a lot of work to make it as easy as possible. In return, volunteers have added support for dozens of microcontrollers (ESP8266, ESP32, STM32, PIC, nRF51, ATtiny, and many other ATmega parts).
The work Adafruit did to add support for SAMD51 is available for everyone to benefit from. They didn't need to get any special permission from Arduino, they just forked Arduino SAMD Boards and made the necessary modifications. Any volunteer is welcome to contribute improvements to that package or work to improve the community support via libraries, example sketches, tutorials, etc.