AFAIK the google chrome (the one from Google, not the free alternative “chromium”) packages are installed to /opt, including a “.desktop” file (which is the part of a package taking care that it will appear in the start menu).
If the package does not have a “post-install” step which refreshes a database of “these are the desktop files available” and/or the path where the desktop file is located is not (yet) in the list of paths the system searches for “.desktop” files, then no entry will be created in the start menu.
However, when logging in next time, one of the standard login scripts (/etc/profile.d/xdg-environment.sh) will take care of that and the entry will appear.