Disney isn't removing the Rivers of America because it's easier than building a path around it.
They're removing because they view it as a waste of space (as so many Disney fans are quick to agree without question).
Disney has gone from removing stores that didn't have a high enough profit margin to retheming lands and reshaping parts of their parks because they don't hit an arbitrary quota.
They're willing to spend billions to remove more of the "park" out of Magic Kingdom Park® because they don't understand their own product, how to manage the land they own or the value of their assets.