Just the design tolerances require it. Best answer I can give you. Maybe UMI or trackbird can elaborate.

LG brackets are pricey but you save time (not cutting) and have options on calipers/rotors/pads. Should you ever need to switch back to stock, you won't have to find spindles and get it all realigned, saving more time. Then again, some people understand the time value of money better than others. Ever done the math on what your time is worth?