While I appreciate your purist take on driving and aspire to be such a disciplined driver one day, there is still a myriad of reasons why one could want to have a functional mic.
I find even the single line: "Hey, I'm driving, call you back later." much better than just ignoring incoming calls.
Also the ecall thing might come in very handy if an accident happens, but that is a very big IF.
I also don't have any need for that, because I never answer or even use my phone while driving.