The carbonation is one thing, but your saliva has lots of buffers to maintain pH.
There's usually a pile of acid added for "tartness" to sodas that lower pH, which overwhelms the buffers.
Often, it's phosphoric acid. Phosphoric acid will quickly react with any free calcium to form insoluble calcium phosphate which will mostly go right through you. So not only are you robbing your mouth of calcium you're also robbing the re-supply process.
There's usually a pile of acid added for "tartness" to sodas that lower pH, which overwhelms the buffers.
Often, it's phosphoric acid. Phosphoric acid will quickly react with any free calcium to form insoluble calcium phosphate which will mostly go right through you. So not only are you robbing your mouth of calcium you're also robbing the re-supply process.