The 8th Doctor doesn’t really remember being in the tardis. Can we really blame him?
We recently learned that Peter Capaldi turned down the audition for playing Doctor Who. If Paul McGann doesn’t remember it and has said that he wasn’t really ever a big fan, then it is easy to see how a true fan may have to turn it down.
If you can barely remember it, if you can’t ever really make the role your own, if your time in such a classic role is really so short….then you cannot really love playing it.
Capaldi was also probably hoping that a more popular celebrity at the time would issue the return of Who, or at least bring the subject up. Unfortunately we had to wait until 2005.