Because the 24-70 is just not wide enough for some shots ...
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... and I can't justify nearly twice the cost for the 14mm prime.
heck I can't really justify the 16-35 for only a few races, but i am sure it will find other uses !

Maybe I could have taken the OM-D as well and used the 7-14 (14-28) Panasonic lens.
But I didn't want to carry two camera systems.