This improves performance. For example
reloadAccess() can otherwise cause fetching all sites the user has permission to over and over again. Even in a simple report we often do reload the same access > 5 times. Sometimes much more.
It should not be done in
reloadAccess() itself since there are actually reasons when you want to reload the access if though the current user is already authenticated. For example when adding a new site: https://github.com/piwik/piwik/blob/master/plugins/SitesManager/API.php#L564