There's a problem, but not with the approval/disapproval axes. It's with the time axis.

Note that we're looking at days 0 - 1,000, that is, less than a 3-year range. This completely overlooks the second term of 2-term presidents. So, for example, we're seeing GWB's post-9/11 boom but not his later ignominy, and we're not seeing Reagan after he got the economy sorted.