Project Access for Security Admin

As the security admin I handle all security for users, adding/modifying fields & workflows etc...I recently did a push 'sync' to all the projects for some new fields that were requested (we are ensuring all projects use the same template). I later found out that there were some projects that I didnt have access to therefore they didnt not get the latest updates. My question is as a security administrator why cant I have access to everything without the person who created the project (usually BA or PM) having to add me?



I am confused by the Security Admin Group vs. Security Admin for a project. I found I had to check that box for certain users to be able to add team members to their projects they created. This opened the users to set themselves as security admin in the group as well. What really is the difference?



Any information would be appreciated.



Thanks

Liana