There are microcontrollers with only 128 bytes of ram and 1KB of flash. They don't have enough memory to support malloc, so there is nothing to garbage collect

There are microcontrollers with only 128 bytes of ram and 1KB of flash. They don't have enough memory to support malloc, so there is nothing to garbage collect in the first place. There isn't enough flash to even store the garbage collector's code, even if it sits unused.