The Beracha Of Al Nitilas Yadayim

The halacha is that when we wash our hands for bread, we make the beracha "al nitalas yadayim" only after we wash our hands. The Mechaber explains that even though we have a rule to make our berachos "oveir la’asiyasan", before we do the mitzvah, this case is different. Since our hands might be tamei or have touched unclean places, we wait until after we wash our hands to make the beracha.
My 9 year old daughter asked me the following question. Why does this chashash only apply to al nitilas yadayim? Every time we need to make a beracha, we should have to wash our hands in case our hands are dirty. Yet we don’t find that we are makpid to wash our hands before making a shehakol or mezonos. Why not? Any Answers?