We know that Moshe did not strike the Nile to turn it to blood because the river had protected him as a baby when his mother sent him floating downstream in his little basket. We know that Moshe did not strike the ground because it was in the ground that he had hidden the body of the Egyptian that he killed. This was Moshe's expression of hakaras ha'tov even to the inanimate objects that had done good for him.
Why is hakaras ha'tov so intertwined with the story of yetzi'as Mitzrayim? See my wife's post here.
And since I am mentioning blog posts by family members, see my son's posts here.