Because it @#%&'s!
Actually. it used to be a feature of UG, but nearly everyone I know complained about it and turned it off, so there probably really wasn't much point in continuing to offer it.
If I'm working on a large part or assembly, and trying to accomplish a complicated task, the last thing I want is for the file to save itself automatically. If it is an assembly, does it save only the work part or the whole assembly tree? What if I had edited some components of the assembly but wasn't sure if I had found the right solution? I realize that you could be able to go back to previous save levels, but it still seems to be too interuptive to me to be worth much. Self discipline (save early and often) is a much better solution in my opinion.
For what it's worth, you can use the save reminder if you want. A better, less aggressive solution. I turn that off though, too.
Believe it if you need it or leave it if you dare. - [small]Robert Hunter[/small]