If you search "tire wear" you will see lots of threads on this. The X5 has a few degrees of negative camber, that is, the rear wheels tilt in wards. This causes excessive wear on the insides of the tires, and is more pronounced with the wider tires. The only things that can be done is to have a mechanic dial out as much camber as possible, and maintain your tire pressures to stated amount. If your tires are not unidirectional, you can have them reversed halfway through their lives.

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2013 X5 3.5i M Sport
2004 M3 cabriolet SMG