Board Thread:General Discussion/@comment-4884084-20150818050852/@comment-34326521-20150828145336

The Omnitrix preventing Ben's death was a literal Deus ex machina (God from the machine). It had never displayed that ability before, and Ben has always been afraid of dying.

As for getting his "life force" taken, it was his soul; Charmcaster then offered it (as well as a bunch of other souls) to Diagon, remember? Besides, what exactly is the difference between "life force" and "soul"?