No really good reason. To my ear, "in case" in this context implies that this well might occur. I think "if" would be be appropriate if under normal conditions this would not be expected.
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CliveYou might like to also consider what you would do if your mother said this to you.I see your point. So the long and the short of it is that the OP does not present an acceptable usage of "in case of," and the writer's intention (in view of the one/
"In the case of rain, take your umbrella".
This is not the same as 'In case of rain . . '.