Breaking buckles is rare? That's not true at all. It may be true for you, but it's not true on a global scale. After grip pads, buckles are our most requested spare part. That the BOA system has a breakaway feature will without question reduce the number of broken BOA dials.It's ready because of questions and concerns about something that is not exceedingly rare. Whereas broken buckles are exceedingly rare. So yes, having parts ready for if it happens with BOA is better than not. But it being so rare as to not really be a thing would be even better.
The force it takes to break the BOA dial will totally nuke a buckle and/or its baseplate. So if you aren't in the habit of breaking buckles, then you won't be breaking BOA dials.