Pro's ride what their sponsors tell them to ride. Wide rims are still fairly new, most big manufacturers (re: sponsors) have not really got into the game yet.
True, but there is more to it than that.
I'm not sure if this makes sense, but…
You still want some compliance in your rims/wheels/tires. Super wide rims take away from that compliance by making the tire sidewall profile too "square" and thus too stiff. Its hard to explain, but that tire sidewall bulge you'd normally get with narrower rims allows the tire to deform without having to use less pressure. Wide rims (ones that are nearly as wide as the tire) are too responsive to side impacts and thus they deflect too much. Does that make sense?
Without sounding overly douchy, this is the main reason why racer types don't like wide rims. And I think that's why they are being marketed more towards recreational riders than racers.