A clear example of why it is a pro is the index of a for loop. Why would it be more maintainable to declare all for loop indexes at the beginning of a function? They are basically bound variables that are only meaningful within their loop, and they are usually not even worth commenting.
More often than not, when maintenance really matter and juniors really choke, the algorithms that powers core functionality usually have nested loops and conditionals. So if you start using inline variable declaration you really have a hard time "where did this was declared". Combine that with compiler switches and you have a recipe for disaster when declaring inline variables vs. a clear section of variables right after function header, where you put all comments to specify what those variables do.
Remember, initial phase of a project is only 10% of it, the maintenance and expanding its functionality is the rest of 90%. Inline variable declarations are a real PITA for that phase.
