Easy fix. The piece is readily available at your dealership. I think they cost $10-20ish. Dealer should pop it on for you, but if they won't its really easy. You can take a piece of that plastic packing ribbon that goes around boxes to hold them together and easily pull the emblem off. The new one simply presses into place. When you pull the old one off there are two prongs that go into gromets on your hood to secure the emblem. If they break off you can simply push them in and put the new emblem on top.

 

Very common problem. I have had 5 BMWs (still have 4), and it has happened on 3 of them. Nothing you did, just age ... and, I suspect the effects of blazing sunlight ... but, just a guess.