There was this from a recent Apple Discussion Forum reply. The thread is here.There has to be more to it than that.
andIf your e-mail address was associated with the ID in any way, for example as a Reachable at or Rescue e-mail address, then it can't be reused with another Apple ID for approximately one year. I have also seen posts that stated Apple told them there was a 30 day waiting period before the address could be used again. You will need to get another e-mail address to use as your Apple ID.
Don't create a new ID, do a name change. That way you will retain access to your data and purchases.
If you are getting a message that the ID you are trying to change to is not available, it means that the ID in question is either set up as a Rescue email address on your current or another Apple ID, or that the address in question has been used for an Apple ID within the last year.