Because the wheels were designed for tubeless tires BMW used a softer, less brittle aluminum alloy.
A harder alloy has the danger that on a hard impact the rim can crack and cause a rapid loss of air pressure. Needless to say, this can be very painful at high speed. A softer rim will deform on a hard impact, but it will keep holding air, and can be repaired if one goes about it slowly and carefully.
As was mentioned, a heavy hammer and a couple wooden blocks with a little patience is all that you need to get the wheel back to reasonably close shape.