Why can't we set the had-figures using AtEndDocument?

[eyalroz]

In iitthesis.cls, I would like to have the following:

\AtEndEnvironment{figure}{\gdef\iitthesis@havefigures{}}
\AtEndDocument{
 \ifdefined\iitthesis@havefigures
  \label{iitthesis:had-figures}
 \fi
  % etc. etc.
}

... but this doesn't work for some reason. Instead, what I actually do is:

\newcommand{\makebackmatter}{%

 % This _should_ be done AtEndDocument, but that fails for some reason
 \ifdefined\iitthesis@havefigures
  \label{iitthesis:had-figures}
 \fi
 % etc. etc.

Why does the former way of doing it not work?