Not only is it what the sponsors provide and pay them for but this as well.
A pro clips in one time in order to do his entire days ride (unless he has problems). We how ever are not as lucky. I don't have a guy who gets me new water bottles everytime mine run dry. I can't grab a lunch on the fly from someone standing on the side of the road with a bag with my name on it. I can't just ride through every intersection all day long because they are closed to car traffic. When my friends and I get separated we don't just ride for hours not caring if they ever catch up.

In other words we have to clip in and out many times, maybe even more so on supported rides. I might even like the SPD's I took off my bike if I only had to get into them one time per day. In the mean time I'll stick with my no look, no fuss Speedplays.