The point of having a ringtone that sounds different from others' ringtones is that you can recognize by its sound that it is your phone that's ringing, when it does. To be able to recognize your own ringtone it needs to be reliably the same every time. Shuffle that ringtone and you will never recognize by its sound that it is your phone that's ringing. You will only know that it's your phone that's ringing when you see it light up. I.o.w. in that scenario a ringtone is totally useless, really just noise pollution, and only causes confusion all around. It also takes longer to answer calls.