In addition : The end-date of a PhD is indeterminate (at least in the UK), since one doesn't know for sure whether the thesis defense will require any re-writin

In addition : The end-date of a PhD is indeterminate (at least in the UK), since one doesn't know for sure whether the thesis defense will require any re-writing, etc. So it's difficult to have a job fixed up completely on the day the magic letter arrives.