ASR is a hugely complex process that is handled by ML algorithms on Amazon's servers. The echo simply does not have the hardware to handle this on it's own.
Is it though? Not trying to be argumentative but I remember using dragon naturally speaking to do voice dictation way back in like 98 on a processor that makes today's average smartphone look like a supercomputer. I thought all the ML stuff was for figuring out context and the like, but straight transcription?