how could the bolts holding the upper control arm to the frame come loose

What is your question?

the bolts holding the front upper control arm to the subframe came loose enough to cause wear to the hole in the subframe. the only fix is to replace the frame, as the frame is aluminum the dealer said it could not be repaired??? How could this happen? The car is just off warranty with less than 30,000 miles, and we are looking at a cost of $2500 for the repair. any suggestion?